IMPALA-1029: DROP DATA SOURCE should remove jar from lib caches

Change-Id: I2a3f0f4e54474aa4fd4e0515bfcdc272d1535544
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2846
Reviewed-by: Matthew Jacobs <mj@cloudera.com>
Tested-by: jenkins