Replace openstack.org git:// URLs with https://

This is a mechanically generated change to replace openstack.org
git:// URLs with https:// equivalents.

This is in aid of a planned future move of the git hosting
infrastructure to a self-hosted instance of gitea (https://gitea.io),
which does not support the git wire protocol at this stage.

This update should result in no functional change.

For more information see the thread at

 http://lists.openstack.org/pipermail/openstack-discuss/2019-March/003825.html

Change-Id: If39f30fe67ab6a95df5cbfb00cdc2cb1eb77e5d0

CONTRIBUTING.rst

@@ -2,7 +2,7 @@ Contributing
 ============
 
 To browse the latest code, see: https://git.openstack.org/cgit/stackforge/gertty/tree/
-To clone the latest code, use `git clone git://git.openstack.org/stackforge/gertty`
+To clone the latest code, use `git clone https://git.openstack.org/stackforge/gertty`
 
 Bugs are handled at: https://storyboard.openstack.org/#!/project/698