upgrade: stop the upgrade with unavailable files
upgrade: stop the upgrade with unavailable files

Explictly raising an exception to stop the upgrade
procedure if one of the files we are going to move
to the shared storage is unavailable.

Change-Id: I313b3d1f3d6091236c2438673e8a7339d3491525
Bug-Url: https://bugzilla.redhat.com/1367732
Signed-off-by: Simone Tiraboschi <cb03129c66ba4da7ba7044049d0f43907bf857bb@redhat.com>

oVirt/ovirt-hosted-engine-ha,oVirt/ovirt-hosted-engine-ha,oVirt/ovirt-hosted-engine-ha,oVirt/ovirt-hosted-engine-ha