Determine which commands a user can access and restrict the CLI

An idea. The nova cli provides a bunch of commands for user and admin usage when it seems like it could almost query keystone to see who the calling user is and restrict commands that are available (in help, and such) based on the information that keystone presents as 'possible' to be called in the first place. This would avoid confusion as to why admin commands are shown for users who could not call them in the first place anyway.