Remove many references to github

OpenStack's primary git repositories aren't on github, so update the
URLs en-masse to point to git.o.o. There are some references left as
they either reference code that is only on github, or require it,
like the Jenkins element.

Change-Id: Id50f2e0fc0b301b5b2d04f769d032044cd11404c
Merge "Remove many references to github"