Allow Cross Server Redirects in https staging

[oldpatricka]

This is disabled right here: https://github.com/nimbusproject/nimbus/blob/master/control/src/python/workspacecontrol/defaults/imageprocurement/propagate_https.py#L185

I don't see any reason we shouldn't allow this. Does anyone have any objections?

[oldpatricka]

As discussed on Campfire, the solution to this will be:

• Print a warning when a cross-server redirect is followed
• Add an option to disable cross server redirects
• Add a warning in the whitelist section of global-policy.conf that redirects can be followed.

[oldpatricka]

This issue is fixed in c611a8f2c33607162b162e52b465755ea16d22b2 (and 2652487b92f777af09398d3bbcc451d16e745050, sigh)