Display a message on the login page

In some cases, particularly when having to log the user out after
performing some action (e.g. password change), we want to display a
friendly message on the login screen to explain to the user why they
have been redirected to the login page.

This adds a function to do so, and uses it in a couple of places:
 - When updating one's own password using the Settings panel
 - Session time out
 - HTTP 401

Change-Id: Ie53c5552159304e1f1304ac6211b3accfd9aa623
Implements: blueprint messages-on-login-page
Add Cisco N1K plugin support in Horizon

This adds Horizon capability to configure and
use network profiles and policy profiles
on the Cisco Nexus 1000V to be used with
networks and instances as is done via neutron
CLI.

To turn on the new dashboard the local_settings
file needs to turn the profile_settings NEUTRON
config variable to cisco.

TODO items include creating a better palate
of unit tests that will run not only when
the cisco n1k subplugin is being used but
in default setting as well.
Need to remove the conditional statements
in the unit tests and make it inclusive.
Additionally need to get a better solution
for how the dashboard/panel registration will
work. Should it be a boolean or check for vendor
specific names.
Also some cleanup and refactoring of commonly
used code everywhere.

Implements: blueprint horizon-cisco-n1k

Change-Id: If6e797ac28c8486cfa92e02742c409d193d9ec84
Merge "Add Cisco N1K plugin support in Horizon"
Merge "Display a message on the login page"