Reduce memory needed to create Ranger policy engine

Ranger policy engine creates a RangerPolicyResourceMatcher object for every resource specified either in policy or in a tag association. PolicyResourceMatcher, for the services that have more than one level in their resource hierarchy, consists of RangerResourceMatcher objects for each level in the resource-level hierarchy for the resource. In many cases, this leads to creation of multiple RangerResourceMatchers with identical resource specification.

This Jira avoids creation of multiple RangerResourceMatcher objects by maintaining a cache of them in the RangerPluginContext object associated with the Ranger policy engine, thereby reducing policy engine's memory needs.