Add some details about trust relationships

This adds the following things:
 - Unauthenticated API endpoints
 - trust REST API
 - Failure scenari related to SSL for the client
 - "lxc config trust" to the command line
 - Update some "lxc config" commands to support querying/setting server
   settings.
 - Fix some consistency issues.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>