* Make sure the chroot container distro version matches the host distro version
due to incompatibilities when mixing distro versions. (LP: #1592117)
* Only set the LXC log file config if the container is already defined.
(LP: #1595239)
* Make sure the directory where ContainersConfig.json lives exists before
trying to write out the file.
* Define XDG_RUNTIME_DIR environment variable for python container testing.