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 .

lib/vmpooler/providers/gce.rb

@@ -86,8 +86,8 @@ module Vmpooler
           return provider_config['machine_type'] if provider_config['machine_type']
         end
 
-        def dns_zone
-          provider_config['dns_zone']
+        def domain
+          provider_config['domain']
         end
 
         def dns_zone_resource_name
@@ -459,7 +459,7 @@ module Vmpooler
         def vm_ready?(_pool_name, vm_name)
           begin
             # TODO: we could use a healthcheck resource attached to instance
-            open_socket(vm_name, dns_zone || global_config[:config]['domain'])
+            open_socket(vm_name, domain || global_config[:config]['domain'])
           rescue StandardError => _e
             return false
           end

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' ]

vmpooler.yaml.example

@@ -75,10 +75,11 @@
 #   - dns_zone_resource_name
 #     The name given to the DNS zone ressource. This is not the domain, but the name identifier of a zone eg example-com
 #     (optional) when not set, the dns setup / teardown is skipped
-#   - dns_zone
-#     The dns zone domain set for the dns_zone_resource_name. This becomes the domain part of the FQDN ie $vm_name.$dns_zone
+#   - domain
+#     Overwrites the global domain parameter. This should match the dns zone domain set for the dns_zone_resource_name.
+#     It is used to infer the domain part of the FQDN ie $vm_name.$domain
 #     When setting multiple providers at the same time, this value should be set for each GCE pools.
-#     default to: global config:domain. if dns_zone is set, it overwrites the top-level domain when checking vm_ready?
+#     (optional) If not explicitely set, the FQDN is inferred using the global 'domain' config parameter
 # Example:
 
   :gce:
@@ -86,6 +87,8 @@
     zone: 'us-central1-f'
     machine_type: ''
     network_name: ''
+    dns_zone_resource_name: 'subdomain-example-com'
+    domain: 'subdomain.example.com'
 
 # :pools:
 #