Support non-rackspace Swift

I'd like to use django-cumulus with my own openstack/swift/keystone infrastructure - and it seems that support for non-rackspace swift has eroded in django-cumulus. This is my attempt to start bringing it back in :-)

If you don't consider yourselves upstream, just let me know and I'll try at richleland's repo instead - the lincolnloop repo just has more activity. Have you tried upstreaming your changes?

The two main issues were:
 * Extra settings required for pyrax.set_setting (tenant_id and auth_url) when using non-rackspace swift
 * pyrax assuming cdn availability (I've also created a pull-request to fix that upstream, but provided a work-around here).

With that, I'm able to use the storage and run the management commands, and with some effort, get the tests passing with non-rackspace swift (urg, those tests are in serious need of a test double... not your issue I know, just interested if it's something you've toyed with or thought about yet).

I've tried to rework the container commands to be more general, and only branch to pyrax-only code for cdn-related functionality.

Again, let me know if you're not interested in merging non-rackspace support/functionality - I'd just like to be able to work on the swift support with others interested in getting it going :-)