Use region specific endpoint when updating s3 hostname

This fixes an issue when using govcloud regions,
as `s3.amazonaws.com` won't map to the govcloud region.

All botocore/awscli unit/integ tests pass
Keep a list of restricted regions that aren't remapped

Fixes an issue when using the govcloud region for s3.
Merge branch 'fix-s3-host' into develop

* fix-s3-host:
  Keep a list of restricted regions that aren't remapped
  Use region specific endpoint when updating s3 hostname