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: Ia58fa2a5350d2c4d9dc8b54ac76a902005f85f30

doc/source/devref/development_environment.rst

@@ -34,7 +34,7 @@ Getting the code
 
 Grab the code::
 
-    git clone git://git.openstack.org/openstack/networking-powervm
+    git clone https://git.openstack.org/openstack/networking-powervm
     cd networking-powervm
 
 Setting up your environment