HTTPretty: Bump to 0.8.0
HTTPretty: Bump to 0.8.0

The 0.8.0 release brings full support for Python 3.

Change-Id: I7237c986efffa0474f7d76bca69a08a26b21adbd
Closes-Bug: 1249165

citrix-openstack-build/keystoneauth,jamielennox/keystoneauth,sileht/keystoneauth