[PATCH][SRU][Disco] shiftfs: simplify passthrough verification

[Thadeu Lima de Souza Cascardo]

Hi, Christian.

TL;DR: why should we apply this fix at this point of the release?

Is this bug upstream at all? If not, it should have a subject of "UBUNTU:
SAUCE".

The main issue with this submission is that it does not have a buglink with a
bug that follows the SRU process, that is, has a good description of the
impact, regression potential and what test has been done for both the fix and
those potential regressions.

Thanks.
Cascardo.