Compatibility of gce.py (Google Cloud Ansible inventory) with Python 3 (#26032)

* Compatibility of gce.py (inventory) with Python 3

* Revert './secrets.py' file check (will import 'secrets' from PYTHONPATH)

Instead of checking if secrets.py exists in the current directory, this
commit will make gce import 'secrets' from one of PYTHONPATH's paths.

There are 2 possibilities:
1. secrets.py will be used if secrets.GCE_PARAMS and
secrets.GCE_KEYWORD_PARAMS are declared.

2. secrets.py will be ignored if secrets.GCE_PARAMS and
secrets.GCE_KEYWORD_PARAMS aren't declared. This could happen in Python
>=3.6 where a module named 'secrets' could be imported if a custom
secrets.py doesn't exist in PYTHONPATH.
Check out https://www.python.org/dev/peps/pep-0506/ and
https://docs.python.org/3/library/secrets.html for more information.

contrib/inventory/gce.py

@@ -92,7 +92,10 @@ import argparse
 
 from time import time
 
-import ConfigParser
+if sys.version_info >= (3, 0):
+    import configparser
+else:
+    import ConfigParser as configparser
 
 import logging
 logging.getLogger('libcloud.common.google').addHandler(logging.NullHandler())
@@ -213,7 +216,7 @@ class GceInventory(object):
         # This provides empty defaults to each key, so that environment
         # variable configuration (as opposed to INI configuration) is able
         # to work.
-        config = ConfigParser.SafeConfigParser(defaults={
+        config = configparser.SafeConfigParser(defaults={
             'gce_service_account_email_address': '',
             'gce_service_account_pem_file_path': '',
             'gce_project_id': '',
@@ -271,10 +274,11 @@ class GceInventory(object):
         # exists.
         secrets_path = self.config.get('gce', 'libcloud_secrets')
         secrets_found = False
+
         try:
             import secrets
-            args = list(getattr(secrets, 'GCE_PARAMS', []))
+            args = list(secrets.GCE_PARAMS)
-            kwargs = getattr(secrets, 'GCE_KEYWORD_PARAMS', {})
+            kwargs = secrets.GCE_KEYWORD_PARAMS
             secrets_found = True
         except:
             pass