lxc: Clean up namespace mounts

5f697f64e5c445ba1b62c82d9167fd6b9c7256d2 introduced a regression
when using lxc containers with qcow2 and qemu-nbd.

When removing the rootfs from the host namespace, it would
terminate the qemu-nbd process as well. This would cause
the kernel too oops under Ubuntu 13.04. Since the underlying
device thtat the libvirt_lxc process disapears.

To get around this we just clean up the host namespace if the
instance is powered-on. When the instance terminates it will
teardown the whole container.

This fixes LP: #1115786

Change-Id: I98bec2338cb455dbd277295ab36767149e05634c
Signed-off-by: Chuck Short <chuck.short@canonical.com>
Merge "lxc: Clean up namespace mounts"