IMPALA-2510: Temp fix for failed TestHdfsCachingDdl test
IMPALA-2510: Temp fix for failed TestHdfsCachingDdl test

This is a temporary fix to unblock impala-cdh5.5x-repeated-runs test.
The root cause is IMPALA-2518 in which the DROP DATABASE with CASCADE
does not remove the cache directives of deleted tables.

Change-Id: I1cf05fbc5d64933182188c76dd6f68d4fbaee02a
Reviewed-on: http://gerrit.cloudera.org:8080/1221
Reviewed-by: Dimitris Tsirogiannis <285e4b680d94e4ded69b0d5c81922fd12d83ee6c@cloudera.com>
Tested-by: Internal Jenkins

cloudera/recordservice,cloudera/recordservice,cloudera/recordservice,cloudera/recordservice,cloudera/recordservice,cloudera/recordservice,cloudera/recordservice