Token-based authentication support for Lava components

We want to add the ability to generate a token that allows authenticated XML-RPC apis calls to the Django-based components of Lava.

For now we will (slightly) abuse HTTP Basic auth (over SSL) to communicate the token to the server -- this is very very easy because the standard library xmlrpclib supports Basic. The server side will be part of linaro-django-xmlrpc (and not a middleware).

Also see https://blueprints.launchpad.net/linaro-django-xmlrpc/+spec/other-o-linaro-xml-rpc-auth-tokens