Add a test for each of report/ignore/stop.  The tests use blkdebug
to generate an error in the middle of a script.  The error is
recoverable (once = "on") so that we can test resuming a job after
stopping for an error.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>