project specific flavors support

Currently flavor (instance type) settings in Nova are shared by all projects. However, there're cases in private cloud deployments that project specific flavor settings are necessary.

In contrast to global flavor setting, project specific flavor is visible and available for specific project only.

* flavor type is public by default, which is accessible to all projects
* non-public flavor type (project specific flavor, or private flavor) is only accessible to those project on the access list, and invisible to all other projects
* admin user is able to query all flavor types ( public flavor by default )
* project members could list all public flavor types and current project specific flavor types

API Extension
--
GET v2/{tenant_id}/flavors/{flavor_id}/os-flavor-access list of project with access to flavor
POST v2/{tenant_id}/flavors/{flavor_id}/action add / remove project to flavor access list

Also implements client bindings for project specific flavor management

Command Use
--
nova flavor-access-list --flavor flavorid return access list of specified flavorid
nova flavor-access-add flavorid projectid add project to private flavor's access list
nova flavor-access-remove flavorid projectid remove project from private flavor access list