[CRIU] tests for automounting

[Tycho Andersen]

Hi Andrey, Pavel,

Here are some tests for automounting; they check external sharing, external
masters, and one test (that currently fails) checks the case Oleg pointed out
where criu is too greedy matching external mounts.

The last case has quite a hack in zdtm.sh; I played around with this for a long
time last night and I couldn't figure out how to do this in a nicer way, but
I'd welcome suggestions. Other than that, I think the rest of the series should
be ok.

Tycho