Add .travis.yml to automatically run Travis-CI on each commit / pull request

To avoid accidentally breaking the testsuite in the future. For this to work, you need to setup the "Travis" service hook under https://github.com/gabrielhurley/django_openstack_auth/settings/hooks. For that you need to register at https://travis-ci.org and sync github repos / enable travis for django_openstack_auth.

Results will look like https://travis-ci.org/saschpe/django_openstack_auth/jobs/8614996. BTW, the testsuite issue is fixed with https://github.com/gabrielhurley/django_openstack_auth/pull/45