packaging: do not use /var/tmp for engine

/var/tmp is intended for temporary files.

The engine is a long-running process, and should not keep its files
there. Use /var/lib/ovirt-engine/jboss_runtime instead.

Change-Id: I88563c8c0d319eb3356b47233a31c82d9e8b84c7
Signed-off-by: Yedidyah Bar David <didi@redhat.com>