Passing options to Rackspace authenticated_url

[duhast]

Hi!

This update allows to pass additional options to Rackspaces authenticated_url.
Options are described here.

Corresponding fog PR is fog/fog#3665

[bensie]

@duhast Does this require bumping to the latest Fog for that method signature to be accepted?

[duhast]

@bensie Ideally yes, but in case the current version is used, nothing should break but these special Rackspace options will just be ignored by fog.

I've asked fog guys when they are going to make a release here