Document source location as git.openstack.org

Change-Id: If7a2801e8c0a6771e9c3ecf1773b449fdd23030a
Prefer .gitconfig username

We should check first the .gitconfig username and then the
environment variables. Otherwise, the .gitconfig username is never
used.

Bug: #1223676
Change-Id: I3b7efd53e1e561108b42a471ddcebfd87984922b
Merge "Document source location as git.openstack.org"
Merge "Prefer .gitconfig username"