Replace git.openstack.org URLs with opendev.org URLs

Thorough replacement of git.openstack.org and review.openstack.org URLs
with their opendev.org counterparts.

Change-Id: I88e894db7b854d32593c770f5aa9b8a91fad7866
diff --git a/REVIEWING.rst b/REVIEWING.rst
index 31fedce..498ce66 100644
--- a/REVIEWING.rst
+++ b/REVIEWING.rst
@@ -187,4 +187,4 @@
   Note that such a policy should be used judiciously, as we should strive to
   have two +2's on each patch set, prior to approval.
 
-.. _example: https://review.openstack.org/#/c/611032/
+.. _example: https://review.opendev.org/#/c/611032/