More precise catch in block volume create.

Narrow the exception when failed to deactivate a new created
volume.

Change-Id: I5ac32eb0d58404c3e066dc73488ae0101560a919
Signed-off-by: Eduardo <ewarszaw@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/18883
Reviewed-by: Yeela Kaplan <ykaplan@redhat.com>
Reviewed-by: Ayal Baron <abaron@redhat.com>
Reviewed-by: Saggi Mizrahi <smizrahi@redhat.com>