Merge juju-info-at-registration [f=1229630] [r=bjornt,ack] [a=Adam Collard]
Add Juju information at registration time.
* Changed schema of JUJU_INFO message to be strict about the keys
* Re-used schema for REGISTER and REGISTER_CLOUD_VM messages
* Added l.lib.juju as resting ground for json parsing and error handling
* Moved juju_filename to main config object, not just specific to monitor