Cleanup and re-enable some tests in TestPartitionMetadata

Partition metadata tests were marked as xfail because of IMPALA-624. Additionally, we had
to invoke hive to insert into two partitions pointing to the same location (this
limitation is now removed). This patch changes the test to use Impala exclusively,
removes the xfail tag and adds a teardown method to the test class.

Change-Id: I15fa97bef4f8714d0873a9c713627a198f3388ad
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2086
Reviewed-by: Ishaan Joshi <ishaan@cloudera.com>
Tested-by: jenkins