[Review Queue] heat

[Liam Young]

Make instance_user configurable for Heat
https://code.launchpad.net/~macgreagoir/charms/trusty/heat/instance_user/+merge/276499

Needs fixing:

Enable integration with hacluster. Looks good but needs some tweaks to 
unit and functional tests.
https://code.launchpad.net/~cbjchen/charms/trusty/heat/next-ha/+merge/280946

Thanks to macgreagoir and cbjchen for their merge proposals!
Liam