Move to oslo-config and update common. Also add missing provider_method to get.
Merge branch 'master' of ssh://github.com/billingstack/billingstack
Multiple changes

* Support Plan and PlanItems in storage
* Make merchant id optional when listing customers.
* Disable Provider in Plan for now.
* Remove unneeded attribs in PlanItem
* Make saving the row optional when calling _save().
Use experimental branch for now.. Fixes issues with nested controllers