avoid waiting for event forever

When executing put request to vdsm in order to upload data to image, in
case of exception before a task was started we may wait for the event
forever, if no task was created there's no need to wait and the error
can be returned immediately.

Change-Id: I04fdd4e6babad93ba69c2ac377f5489c5be21584
Signed-off-by: Liron Aravot <laravot@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/27977
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>