Adding django kwargs to login and logout views

The django.contrib.auth.views login and logout views take usefull parameters
which where dropped by the openstack_auth.views methods.

Added a TOKEN_TIMEOUT_MARGIN which allows to check token expiration minus a
time margin in seconds. This is usefull if you know a process will take a
certain time, you want to have your token still valid all this time (e.g. the
time it can take to render a view).

This patch is required for https://review.openstack.org/88220

Change-Id: I7508c40d6f1eaa2bf1eef5cc762052b15d6d9273
Closes-Bug: 1308918