Add Apache 2 license.

Change-Id: Ic8384ef033826a156bd4f7907af818ba2a32e7be
Reviewed-on: https://review.openstack.org/25925
Reviewed-by: Jesse Keating <jesse.keating@rackspace.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Evgeny Fadeev <evgeny.fadeev@gmail.com>
Reviewed-by: Evgeny Fadeev <evgeny.fadeev@gmail.com>
Tested-by: Jenkins