Interface to Enable dynamic provisioning of the instance resources

Because of the varying workload patterns, some times it is necessary to scale instance resources instead of launching new instances. In this blueprint instead of resizing instance to new flavor we can set quotas to existing flavor (or custom flavor) and vertically scale this resources as per needs.

Proposed changes::
1) Add a new API "live-resize" to be available for instance owners and project
  admins.
2) Add quotas to flavor metadata.(Max- min rages supported for scaling)
3) Client Interface to enable scaling as per the support of different Hypervisor and Guset os combinations( throws Not supported error incase particular guest os has no support for scaling)

Ref:: https://blueprints.launchpad.net/nova/+spec/instance-live-resize