Query Parameters Pruning API and Tests (sonic-net#105)

* Query Parameters Pruning API and Tests

- Pruning API used by subtree transformers for Query Parameters.
- Tests. ( Only ACL is enabled currently, since the others need
  support from the corresponding feature teams )
- Updated the hooks to invoke the pruning API.
- The GET request cancelling context parameter is passed to some
  of the pruning functions, but is not implemented since that is appearing
  in a separate PR

* Query Parameters Pruning API and Tests.
    Fix for missing pruneDone check.

translib/transformer/xfmr_interface.go

@@ -52,6 +52,7 @@ type XfmrParams struct {
 	pCascadeDelTbl       *[]string //used to populate list of tables needed cascade delete by subtree overloaded methods
 	yangDefValMap        map[string]map[string]db.Value
 	queryParams          QueryParams
+	pruneDone            *bool
 	invokeCRUSubtreeOnce *bool
 }