packaging: engine-upgrade - check for free space before upgrade

Add pre-run check to engine-upgrade, so it will verify that enough free
space is available for the upcoming database backup + rpm installation.

Change-Id: I90eae48aea70187dc88c79044a353089f69350a0
Signed-off-by: Ofer Schreiber <oschreib@redhat.com>
Signed-off-by: Alex Lourie <alourie@redhat.com>