mounts: make pivot_root after restoring mount points
mounts: make pivot_root after restoring mount points

We are using tar for resting tmpfs. Currently we execute tar from a
restored root, but nobody guarantees that it is there and that it's
really tar.

We don't have reason to change root too early. Lets live in a source
root as long as we can, because we can be sure that it's consistent.

https://bugzilla.openvz.org/show_bug.cgi?id=2870

v2: remove redundant chdir()
Signed-off-by: Andrey Vagin <74c05afa918858348d6db8037d82fa8124870113@openvz.org>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@parallels.com>

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