accept plan_details from service gateways

Instead of sending just a list of plan names, the service gateway can
now send an array ("plan_details") containing details about the service
plans
This commit adds the "extra" attribute to service plans
Expose ServicePlan#extra
[bugfix] don't filter "free"ness
Refactor legacy_service_gateway_spec.rb
Make "rake spec" the default rake task
[finishes #46157255] Service offering's plans attributes are whitelisted for safety
ServicePlan's #create calls bypass mass-assignment verification
Removing staging task logs and redis.
[#45814227]

Change-Id: I6e72fb3aaf862810043926e36273bd93a4f00213
Attempt to fix a non-deterministic failure on Travis

Our theory is that the temp file object is being garbage collected
before the expectation is executed, which deletes the file on disk and
causes the expectation to fail.