Fix ubuntu-12 issues in LxcHost

* fix incorrect checking for btrfs availability
* do not use -B option when btrfs is not available (create_container)
* add ability to specify distro release in config
* delete stale tunnels
* fix issue when /dev/loop0 is not available

Closes-Bug: #1276949

Change-Id: I4170fb8e51851979d0610493a9d4c656107d750d