IMPALA-642: Conjunctive predicates on HBase table not working...

This commit fixes IMPALA-642 issue where conjunctive predicates are
returning incorrect results from HBase in the presence of NULL values.

The following changes are included:
1. Modified the HBaseScanNode to re-apply the "pushed-down" predicates.
2. Added tests in QueryTest/hbase-filters.test
3. Added tests in PlannerTest/hbase.test

Change-Id: I598b325ad63b043b325fba74448698ed71a3cd78
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2414
Reviewed-by: Marcel Kornacker <marcel@cloudera.com>
Tested-by: jenkins