Enable test 'vbucket deletion doesn't affect new data' under RocksDB

Enable this test under RocksDB as it now passes (spotted when
verifying behaviour of RocksDB for vBucket delete / create).

Change-Id: Ia902d35cb4bc0668642453dde9c14547f1bddcc2
Reviewed-on: http://review.couchbase.org/111896
Tested-by: Build Bot <build@couchbase.com>
Reviewed-by: James Harrison <james.harrison@couchbase.com>

Author: daverigby

engines/ep/tests/ep_testsuite_basic.cc

@@ -2427,9 +2427,7 @@ BaseTestCase testsuite_testcases[] = {
                  test_setup,
                  teardown,
                  NULL,
-                 // TODO RDB: implement getItemCount. Needs the
-                 // 'ep_warmup_value_count' stat.
-                 prepare_skip_broken_under_rocks,
+                 prepare,
                  cleanup),
         TestCase("non-resident decrementers",
                  test_mb3169,