When tests are executed concurrently all of them use
the same root, so libraries must be copied atomically.

Without this patch we can get errors like this:
cp: cannot create regular file ‘/tmp/criu-root.m45u5Y/lib64/ld-linux-x86-64.so.2’: File exists
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>