When blockcommit finishes successfully, one of the
qemuBlockJobProcessEventCompletedCommit() and
qemuBlockJobProcessEventCompletedActiveCommit() event handlers is called.
This is where the delete flag (stored in qemuBlockJobCommitData since the
previous commit) can actually be used to delete the committed snapshot
images if requested.

We use virFileRemove() instead of a simple unlink() to cover the case where
the image to be removed is on an NFS volume.
Signed-off-by: NPavel Mores <pmores@redhat.com>
Reviewed-by: NPeter Krempa <pkrempa@redhat.com>