Move diff and wait to perform_action (#375)

This primarily moves the diff and wait logic from the various service
methods to perform_action to eliminate code duplication. I also moved
the diff_objects function out of the service object and moved most of
the find_resource logic to a new resource client method. We ended up
with several modules creating a service object just to use one of these
methods, so it seemed to make sense to make these more accessible.

tests/unit/module_utils/test_waiter.py

@@ -89,7 +89,7 @@ def test_waiter_waits_for_missing_resource():
         namespace=RESOURCES[0]["metadata"].get("namespace"),
     )
     assert result is False
-    assert instance is None
+    assert instance == {}
     assert abs(elapsed - 3) <= 1