vcs: Add support for git.openstack.org
vcs: Add support for git.openstack.org

Go is being proposed as an officially supported language for elements of
OpenStack:

  https://review.openstack.org/#/c/312267/

As such, repos that exist in OpenStack's git infrastructure
are likely to become places from which people might want to go get
things. Allow optional .git suffixes to allow writing code that
depends on git.openstack.org repos that will work with older go versions
while we wait for this support to roll out.

Change-Id: I1f7be6b7aae63f9c554dbcdbfa46855bcff321df
Reviewed-on: https://go-review.googlesource.com/23362
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/tools,syreclabs/go-tools,golang/tools,golang/tools,golang/tools,syreclabs/go-tools,syreclabs/go-tools,syreclabs/go-tools,golang/tools,syreclabs/go-tools,syreclabs/go-tools