initial commit of 'calling out to Nova for Flavor management' code - UNTESTED - will fix in story next sprint. more info in comments @ ./tuskar/compute/nova.py
Expose Flavor resource as a subcollection of ResourceClass - initial commit

examples @
https://github.com/tuskar/tuskar/wiki/cURL-commands#flavor---this-resource-only-exists-as-part-of-resourceclass
Fix Nits: proper URI for Flavor and expose only those Flavors belonging to a ResourceClass