WHAT
Add a unit test to cover cases where params may not be in the return object from AWS for elasticache UpdateActions.

HOW

Add an additional test case to this test -> https://github.com/integr8ly/cloud-resource-operator/blob/master/pkg/providers/aws/provider_redis_test.go#L2246-L2250 where by the new case has those values empty or not available in the object.

See the additional unit test case added for similar nil possibilities in Postgres here -> https://github.com/integr8ly/cloud-resource-operator/pull/414/files?diff=unified&w=0

If the test case indicates that the logic would fail in the case of any of those parameters being missing then handle that in the code. Using SafeStringDereference might be an option as it's already used in the existing function. 

DONE
Test case is added and the logic in the function passes the case.