[last PR stuff] + Add warning if configs specified in 2 params (#5)

* Lean on API validation for tower_inventory_source arg errors

used for
 - validating needed credential is given
 - missing source_project for scm sources

* Add warning when config is specified in 2 places

Fix up unit tests, address multiple comments re: backwards compatibility, redundant methods, etc.

Update new_name and variables parameters, update unit tests

awx_collection/test/awx/test_credential.py

@@ -78,10 +78,8 @@ def test_create_custom_credential_type(run_module, admin_user):
 
     ct = CredentialType.objects.get(name='Nexus')
     result.pop('invocation')
-    result.pop('name')
     assert result == {
-        "credential_type": "Nexus",
-        "state": "present",
+        "name": "Nexus",
         "id": ct.pk,
         "changed": True,
     }