task/restart: Fix check for done

The last command a restart script outputs is 'done'
indicating the script does not require being restarted
further.  Handle this case properly.

Signed-off-by: Sam Lang <sam.lang@inktank.com>
task/restart:  Cleanup in finally

Need to cleanup the files created for this test from
the testdir.

Signed-off-by: Sam Lang <sam.lang@inktank.com>