snapshot: correct previous snapshot commit

Condition was swapped - however since it's been based on 'random'
memory content it's been missed as attribute has not been set.

So now we have quite a few possible results when testing.

We have old status without separate metadata and
we have kernels with fixed snapshot leak bug.

(in-release update)
tests: updates

Add some vgremove calls.
Remove uneeded test for some unused commands.
Add tests for missing commands.
cleanup: relocate segment flags

Move flags for segments to segtype header where it seems more closely
related as the features are related to segtype and not activation.

Use unsigned #define - since it's more common in lvm2 source code
for bit flags.
tests: drop remove

Generates waaaaay too much log from lvmetad test.

TODO: once we will be able to remove more LVs with a single
write - we may restore....
tests: quote dev
tests: remove extra vgremove

These vgremove calls were not correct.
test: warn rather than fail when %FREE isn't working right

%FREE allocation has been broken for RAID.  At 100%FREE, there is
still an extent left for certain tests.  For now, change the test
to warn rather than completely fail.
nix: Import the modular specfile we use for nix-driven builds.
NIX: Fix build-dependencies for FC 18.
NIX: Grab specfile from lvm2Nix (at least for now).
NIX: Copy collected test results into the output.
NIX: Fix a couple typos in build product handling.
NIX: Make it possible to only run a subset of tests (via T).
NIX: Adapt to use of 9P in VM builds.
NIX: Add an fc18 build that includes fedora updates.
NIX: Add default.profile to the spec file.
NIX: The mergeUsr attribute was renamed to unifiedSystemDir.
NIX: Fix chrooted builds, passing down package lists explicitly.
NIX: Run tests with /dev and (on recent Fedora) with udevd running.
nix: Run udevd in foreground.