packaging: dbscripts: drop index if exists

drop index if exists using fn_db_create_index.

Change-Id: Ibacd60bb90ba6e1213b4f0fcb4844aa36ff60fc7
Bug-Url: https://bugzilla.redhat.com/1155153
Signed-off-by: Yedidyah Bar David <didi@redhat.com>