libxl: resume lock process after failed migration

libxl: resume lock process after failed migration

During migration, the lock process is paused in the perform phase
but not resumed if there is a subsequent failure, leaving the locked
resource unprotected.

The perform phase itself can fail, in which case the lock process
should be resumed before returning from perform. The finish phase
could also fail on the destination host, in which case the migration
is canceled in the confirm phase and the VM is resumed. The lock
process needs to be resumed there as well.

Signed-off-by: Jim Fehlig <jfehlig@suse.com>