core: Adding cleandb.sh script

The script enables to drop all database objects installed by oVirt and
leaving a clean database.

Basic usage:
             cleandb -u <user> -d <database>

Change-Id: I7ff33e4ccb8cb66bbe06f5d1c8a00f22d28a2e31
Signed-off-by: Eli Mesika <emesika@redhat.com>
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>