Allow several base URLs for projects in the gitrepo driver
Allow several base URLs for projects in the gitrepo driver

Previously, the gitrepo driver was hardcoding upstream URLs for
projects to be https://github.com/openstack/$PROJECT_NAME. This is
not working anymore for PBR[1], which is under the openstack-dev
namespace.

As a first step, we are creating a list of potential base URLs and
checking for each project. A follow-up patch could set this as an
option in projects.ini, rather than a hardcoded list.

[1] - https://review.openstack.org/465918

Change-Id: Id63d4be6b1bbccb5dafe7585d13070a28cda357f

openstack-packages/delorean,openstack-packages/DLRN,openstack-packages/delorean,openstack-packages/DLRN