Set sync_ddl=true for tests that drop functions.

This is a temporary "fix" for IMPALA-795 to unblock the build. The
actual fix should prevent a dropped and re-created function from being
re-dropped by an old catalog update.

Change-Id: Id9dc36a8ecd5e7d1a1146ad0ac092ae12cb33529
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1547
Reviewed-by: Skye Wanderman-Milne <skye@cloudera.com>
Tested-by: jenkins