Unlike other hypervisor to directly using image for VM, rootfs need to
be mounted in setup_container() for lxc before launching the domain.
However, this leads to several problems:
* previously spawned container polluted later spawned container, which
in turn causing lvm device refused to be removed, as bug descirbes
* container rootfs not mounted after nova stop/start sequence
This commit addresses above two issues.
Fixes bug 1091639
Change-Id: I718baa6e46cf07a5458a5b80d42139dd353ae51c