Fix import of gce/gcdns without a libcloud module

The module level function defs for gcdns_connect() and
gce_connect() provide a default arg for 'provider' that
references into the libcloud module. If the libcloud
modules were not installed, the gce/gcdns python modules
would throw ImportError.

Let the provider arg default to None and if not provided,
set it to the default libcloud.compute.types.Provider.*
value if the modules are installed.

lib/ansible/module_utils/gcdns.py

@@ -40,11 +40,12 @@ except ImportError:
 USER_AGENT_PRODUCT = "Ansible-gcdns"
 USER_AGENT_VERSION = "v1"
 
-def gcdns_connect(module, provider=Provider.GOOGLE):
+def gcdns_connect(module, provider=None):
     """Return a GCP connection for Google Cloud DNS."""
     if not HAS_LIBCLOUD_BASE:
         module.fail_json(msg='libcloud must be installed to use this module')
 
+    provider = provider or Provider.GOOGLE
     return gcp_connect(module, provider, get_driver, USER_AGENT_PRODUCT, USER_AGENT_VERSION)
 
 def unexpected_error_msg(error):

lib/ansible/module_utils/gce.py

@@ -40,10 +40,11 @@ except ImportError:
 USER_AGENT_PRODUCT = "Ansible-gce"
 USER_AGENT_VERSION = "v1"
 
-def gce_connect(module, provider=Provider.GCE):
+def gce_connect(module, provider=None):
     """Return a GCP connection for Google Compute Engine."""
     if not HAS_LIBCLOUD_BASE:
         module.fail_json(msg='libcloud must be installed to use this module')
+    provider = provider or Provider.GCE
 
     return gcp_connect(module, provider, get_driver, USER_AGENT_PRODUCT, USER_AGENT_VERSION)