[vcloud_director|tests] Fix some edge cases.

tests/vcloud_director/models/compute/helper.rb

@@ -26,7 +26,7 @@ def organizations
 end
 
 def organization
-  organizations.first
+  @organization ||= organizations.get_by_name(vcloud_director.org_name)
 end
 
 def catalogs

tests/vcloud_director/models/compute/media_tests.rb

@@ -6,6 +6,7 @@ VCR.use_cassette(File.basename(__FILE__)) do
     pending if Fog.mocking?
 
     medias = vdc.medias
+    pending if medias.all.empty?
     media = medias.first
 
     tests('Compute::VcloudDirector | media') do

tests/vcloud_director/models/compute/organizations_tests.rb

@@ -6,7 +6,7 @@ VCR.use_cassette(File.basename(__FILE__)) do
     organizations = vcloud_director.organizations
     tests("#There is at least one organization").returns(true) { organizations.size >= 1 }
 
-    org = organizations.first
+    org = organizations.get_by_name(vcloud_director.org_name)
 
     tests("Compute::VcloudDirector | organization") do
       tests("#name").returns(String) { org.name.class }

tests/vcloud_director/requests/compute/network_tests.rb

@@ -9,9 +9,9 @@ Shindo.tests('Compute::VcloudDirector | network requests', ['vclouddirector']) d
     :is_inherited => Fog::Boolean,
     :gateway => String,
     :netmask => String,
-    :dns1 => String,
-    :dns2 => String,
-    :dns_suffix => String,
+    :dns1 => Fog::Nullable::String,
+    :dns2 => Fog::Nullable::String,
+    :dns_suffix => Fog::Nullable::String,
     :ip_ranges => [{
       :start_address => String,
       :end_address => String