core:  unlock_entity.sh fails if pwd is not...

unlock_entity.sh script fails if executed from a directory other than
/usr/share/ovirt-engine/dbscripts

Actually, that's true for all shell scripts under dbscripts dir.
Code was changed to change to the dbscripts directory when a script
starts and restore the original directory upon script completion.

Change-Id: Iceeb2f28ce17dd117ecc2cded79077a9aca5e512
Signed-off-by: Eli Mesika <emesika@redhat.com>