refactor dns_zone to be renamed domain to match the global parameter being overwritten

in the upstream vmpooler code, we use the global domain parameter, so naming that parameter
the same in GCE. This parameter can be optionally set in the provider config, and
overwrites the global parameter. It is used to infer the FQDN as .

spec/spec_helper.rb

@@ -1,11 +1,9 @@
 # frozen_string_literal: true
 
 require 'simplecov'
-=begin
 SimpleCov.start do
   add_filter '/spec/'
 end
-=end
 require 'helpers'
 require 'rspec'
 require 'vmpooler'

spec/unit/providers/gce_spec.rb

@@ -75,7 +75,7 @@ EOT
     zone: '#{zone}'
     network_name: 'projects/itsysopsnetworking/global/networks/shared1'
     dns_zone_resource_name: 'test-vmpooler-puppet-net'
-    dns_zone: 'test.vmpooler.puppet.net'
+    domain: 'test.vmpooler.puppet.net'
 :pools:
   - name: '#{poolname}'
     alias: [ 'mockpool' ]