Fix error on file predefined ACL helpers

The helpers were not working and returning the following error:

    Cannot provide both a predefinedAcl and access controls.

This is because the predefinedAcl was being set and the existing acl rules were
not being overridden. The fix is to provide empty rules so the predefinedAcl
rule can be applied.

[refs googleapis#381]

lib/gcloud/storage/connection.rb

@@ -240,7 +240,7 @@ def download_file bucket_name, file_path
       def patch_file bucket_name, file_path, options = {}
         params = { bucket: bucket_name,
                    object: file_path,
-                   predefinedAcl: options[:acl]
+                   predefinedAcl: options[:predefined_acl]
                  }.delete_if { |_, v| v.nil? }
 
         @client.execute(
@@ -395,7 +395,8 @@ def patch_file_request options = {}
           "contentEncoding" => options[:content_encoding],
           "contentLanguage" => options[:content_language],
           "contentType" => options[:content_type],
-          "metadata" => options[:metadata]
+          "metadata" => options[:metadata],
+          "acl" => options[:acl]
         }.delete_if { |_, v| v.nil? }
       end
 

lib/gcloud/storage/file/acl.rb

@@ -545,7 +545,8 @@ def clear!
 
         def update_predefined_acl! acl_role
           resp = @connection.patch_file @bucket, @file,
-                                        acl: acl_role
+                                        predefined_acl: acl_role,
+                                        acl: []
 
           return clear! if resp.success?
           fail Gcloud::Storage::ApiError.from_response(resp)

test/gcloud/storage/file_acl_test.rb

@@ -383,6 +383,7 @@
   def predefined_acl_update acl_role
     mock_connection.patch "/storage/v1/b/#{bucket_name}/o/#{file_name}" do |env|
       env.params["predefinedAcl"].must_equal acl_role
+      JSON.parse(env.body)["acl"].must_equal []
       [200, {"Content-Type"=>"application/json"},
        random_file_hash(bucket_name, file_name).to_json]
     end