REST endpoints do not prevent duplicate values for a resource resulting in multiple policies for a resource

Ranger UI prevents duplicate values for a resource e.g. while creating hive policy, UI prevents list of duplicate values for database such as [test_db1,test_db1]

When creating policies via REST endpoints, the checks for duplicate values for a resource are not done and results in duplicate policies for the same resource (in this case test_db1).  

Policy validation should be improved to havre this check in place to prevent duplicate values for a given resource.