Code review comment for lp:~rvb/maas/lp-1313550

Looks good. The self.patch calls could probably be rewritten without the "magic string", such as:

    self.patch(uec2roottar.check_output)

(but this was recently landed in 1.9, so if there is a chance this will be back-ported to 1.8, let's leave it as-is.)