Include project_id in authentication

Added support for specifying project_id in authentication. This fixes issue #14. The following testing was performed:

 - Verify that Keystone authentication fails without specifying project_id and without patch
 - Check "help" message for mn-ctl
 - Specify project id and then run "show router" command:
   * Project id loaded from .midonetrc configuration file
   * Project id specified in MIDO_PROJECT_ID environment variable
   * Project id specified as a command argument "-i"
   * Project id specified as a command argument "--project-id"