ovirt: Add env variables to dynamic inventory (#31821)

This patch add new environment variables to oVirt dynamic inventory
to be consistent with all other oVirt modules:

 OVIRT_URL
 OVIRT_USERNAME
 OVIRT_CAFILE
 OVIRT_PASSWORD

Those variables are used as fallback if user don't specify a ini file,
with appropriate variables there.

contrib/inventory/ovirt4.py

@@ -124,10 +124,10 @@ def create_connection():
     # Create parser and add ovirt section if it doesn't exist:
     config = configparser.SafeConfigParser(
         defaults={
-            'ovirt_url': None,
+            'ovirt_url': os.environ.get('OVIRT_URL'),
-            'ovirt_username': None,
+            'ovirt_username': os.environ.get('OVIRT_USERNAME'),
-            'ovirt_password': None,
+            'ovirt_password': os.environ.get('OVIRT_PASSWORD'),
-            'ovirt_ca_file': None,
+            'ovirt_ca_file': os.environ.get('OVIRT_CAFILE'),
         }
     )
     if not config.has_section('ovirt'):