Don't delete a running container.  If it's running, abort the delete
unless a new '-f' (force) flag is given, in which case, stop it first.

Handle the case where we can't find $rootfs in config

Fix broken detection of lvm backing store
Signed-off-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>