Allow configuration of apt repository to avoid 'cloud-archive only supported on precise' errors when running trusty
Fixes for trusty. Determine series. Handle bareword in volume-show.
More intelligence in selecting series
Test that precise installs implicitly get the havana repo
[thedac] Add cloud-archive:havana repo with precise, but not trusty or later, per https://code.launchpad.net/~thedac/charms/precise/block-storage-broker/configure-repository/+merge/226721