Feature/provisioner multitenant

first version of the multitenant provisioner master, required for #212 .  a couple high-level items:
* Docs will be added (working on those now)
* See the diff for some minor changes to the existing provisioner (now: worker)
* For simplicity, added this under provisioner/multitenant folder, and the ruby calls up to '../daemon/provisioner' for the worker.  There will be a followup PR to restructure the provisioner directory.  
* try it out, switch to the branch and from ``provisioner/multitenant`` run:
   * ``./bin/provisioner --uri http://localhost:55054`` (-h for other options, default binding is 0.0.0.0:55056)
   * add workers: ``./spec/tenant_worker_request.rb mytenant 3``
   * delete tenant: ``curl -v -X DELETE http://localhost:55056/v1/tenants/mytenant``
   * get heartbeat stats: ``curl http://localhost:55056/heartbeat``
* basic rspec testing, run rake
* rubocop is happy (2 minor offenses which will be addressed when we iron out the plugin data stuff)



Isn't (at least) provisioner required? Maybe this should be checked in the script, itself... but we should ensure that we have all of the options that we will need.