Fix REXML 3.4.2+ compatibility

REXML 3.4.2+ deprecated accepting array as an element in `XPath.match`
[[1]]. This led to test errors such as:

~~~
  3) VagrantPlugins::ProviderLibvirt::Action::ResolveDiskSettings#call when vm box is in use when box metadata is not available when multiple volumes in domain config should populate domain volumes with devices
     Failure/Error:
       expect(env[:domain_volumes]).to match(
         [
           hash_including(
             device: 'vda',
             absolute_path: '/var/lib/libvirt/images/vagrant-test_default.img'
           ),
           hash_including(
             device: 'vdb',
             absolute_path: '/var/lib/libvirt/images/vagrant-test_default_1.img'
           ),
       expected [{absolute_path: "/var/lib/libvirt/images/vagrant-test_default.img", bus: "virtio", cache: "default", device: "vda", name: "vagrant-test_default.img"}] to match [#<RSpec::Mocks::ArgumentMatchers::HashIncludingMatcher:0x00007fff921b3db8 @expected={device: "vda", absolute_path: "/var/lib/libvirt/images/vagrant-test_default.img"}>, #<RSpec::Mocks::ArgumentMatchers::HashIncludingMatcher:0x00007fff921b3d40 @expected={device: "vdb", absolute_path: "/var/lib/libvirt/images/vagrant-test_default_1.img"}>, #<RSpec::Mocks::ArgumentMatchers::HashIncludingMatcher:0x00007fff921b3cc8 @expected={device: "vdc", absolute_path: "/var/lib/libvirt/images/vagrant-test_default_2.img"}>]
       Diff:
       @@ -1,4 +1,6 @@
       -[hash_including(device: "vda", absolute_path: "/var/lib/libvirt/images/vagrant-test_default.img"),
       - hash_including(device: "vdb", absolute_path: "/var/lib/libvirt/images/vagrant-test_default_1.img"),
       - hash_including(device: "vdc", absolute_path: "/var/lib/libvirt/images/vagrant-test_default_2.img")]
       +[{absolute_path: "/var/lib/libvirt/images/vagrant-test_default.img",
       +  bus: "virtio",
       +  cache: "default",
       +  device: "vda",
       +  name: "vagrant-test_default.img"}]
     # ./spec/unit/action/resolve_disk_settings_spec.rb:200:in 'block (6 levels) in <top (required)>'
     # ./spec/support/unit_context.rb:51:in 'block (3 levels) in <top (required)>'
     # ./spec/support/unit_context.rb:43:in 'block (2 levels) in <top (required)>'
     # ./spec/support/unit_context.rb:51:in 'block (3 levels) in <top (required)>'
     # ./spec/support/unit_context.rb:43:in 'block (2 levels) in <top (required)>'
~~~

This changes the logic in a way, that XPath is matching against whole
XML document, instead of array of XML elements.

[1]: ruby/rexml#252

Author: voxik

lib/vagrant-libvirt/action/destroy_domain.rb

@@ -59,7 +59,7 @@ def call(env)
             domain_xml = libvirt_domain.xml_desc(1)
             xml_descr = REXML::Document.new(domain_xml)
             disks_xml = REXML::XPath.match(xml_descr, '/domain/devices/disk[@device="disk"]')
-            have_aliases = !(REXML::XPath.match(disks_xml, './alias[@name="ua-box-volume-0"]').first).nil?
+            have_aliases = !REXML::XPath.match(xml_descr, '/domain/devices/disk[@device="disk"]/alias[@name="ua-box-volume-0"]').first.nil?
             if !have_aliases
               env[:ui].warn(I18n.t('vagrant_libvirt.domain_xml.obsolete_method'))
             end
@@ -73,7 +73,9 @@ def call(env)
             # the additional storage devices are.
             detected_box_volumes = 0
             if have_aliases
-              REXML::XPath.match(disks_xml, './alias[contains(@name, "ua-box-volume-")]').each do |box_disk|
+              REXML::XPath.match(xml_descr,
+                                 '/domain/devices/disk[@device="disk"]/alias[contains(@name, "ua-box-volume-")]'
+              ).each do  |box_disk|
                 diskname = box_disk.parent.elements['source'].attributes['file'].rpartition('/').last
                 detected_box_volumes += 1
 
@@ -130,13 +132,13 @@ def call(env)
               # look for exact match using aliases which will be used
               # for subsequent domain creations
               if have_aliases
-                domain_disk = REXML::XPath.match(disks_xml, './alias[@name="ua-disk-volume-' + index.to_s + '"]').first
+                domain_disk = REXML::XPath.match(xml_descr, '/domain/devices/disk[@device="disk"]/alias[@name="ua-disk-volume-' + index.to_s + '"]').first
                 domain_disk = domain_disk.parent if !domain_disk.nil?
               else
                 # otherwise fallback to find the disk by device if specified by user
                 # and finally index counting with offset and hope the match is correct
                 if !disk[:device].nil?
-                  domain_disk = REXML::XPath.match(disks_xml, './target[@dev="' + disk[:device] + '"]').first
+                  domain_disk = REXML::XPath.match(xml_descr, '/domain/devices/disk[@device="disk"]/target[@dev="' + disk[:device] + '"]').first
                   domain_disk = domain_disk.parent if !domain_disk.nil?
                 else
                   domain_disk = disks_xml[offset + index]

lib/vagrant-libvirt/action/resolve_disk_settings.rb

@@ -50,18 +50,19 @@ def call(env)
               domain_xml = libvirt_domain.xml_desc(1)
               xml_descr = REXML::Document.new(domain_xml)
               domain_name = xml_descr.elements['domain'].elements['name'].text
-              disks_xml = REXML::XPath.match(xml_descr, '/domain/devices/disk[@device="disk"]')
-              have_aliases = !REXML::XPath.match(disks_xml, './alias[@name="ua-box-volume-0"]').first.nil?
+              have_aliases = !REXML::XPath.match(xml_descr, '/domain/devices/disk[@device="disk"]/alias[@name="ua-box-volume-0"]').first.nil?
               env[:ui].warn(I18n.t('vagrant_libvirt.domain_xml.obsolete_method')) unless have_aliases
 
               if have_aliases
-                REXML::XPath.match(disks_xml,
-                                   './alias[contains(@name, "ua-box-volume-")]').each_with_index do |alias_xml, idx|
+                REXML::XPath.match(xml_descr,
+                                   '/domain/devices/disk[@device="disk"]/alias[contains(@name, "ua-box-volume-")]'
+                ).each_with_index do |alias_xml, idx|
                   domain_volumes.push(volume_from_xml(alias_xml.parent, domain_name, idx))
                 end
               else
                 # fallback to try and infer which boxes are box images, as they are listed first
                 # as soon as there is no match, can exit
+                disks_xml = REXML::XPath.match(xml_descr, '/domain/devices/disk[@device="disk"]')
                 disks_xml.each_with_index do |box_disk_xml, idx|
                   diskname = box_disk_xml.elements['source'].attributes['file'].rpartition('/').last