Avoid exceptions for zone facts on FreeBSD

FreeBSD currently loads all Solaris facts, but FreeBSD does not have
"zones", and the zone related facts fail hardly when being processed.

Improve error detection when building the zone facts, and do not emit
these facts when an error occurred.

lib/facts/solaris/solaris_zones/zone.rb

@@ -21,6 +21,8 @@ def call_the_resolver
           zones = {}
 
           results = Facter::Resolvers::SolarisZone.resolve(:zone)
+          return unless results
+
           results&.each do |result|
             zones.merge!(parse_result(result))
             resolved_facts << create_legacy_zone_facts(result)

lib/resolvers/solaris/solaris_zone_name.rb

@@ -25,6 +25,8 @@ def build_current_zone_name_fact(fact_name)
           end
           @fact_list[:current_zone_name] = zone_name_output.chomp
           @fact_list[fact_name]
+        rescue Errno::ENOENT
+          # zonename is not available
         end
       end
     end

lib/resolvers/solaris/zone_resolver.rb

@@ -27,6 +27,8 @@ def build_zone_fact(fact_name)
           @fact_list[:zone] = create_zone_facts(zone_adm_output)
 
           @fact_list[fact_name]
+        rescue Errno::ENOENT
+          # zoneadm is not available
         end
 
         def create_zone_facts(zones_result)