Install tripleo-common in buildimage jobs
Install tripleo-common in buildimage jobs

In order to pick the latest changes from the yaml we use for
building images, add it to the list of projects to be cloned,
and start using it as the base for image builds.

Change-Id: I78bcc0dd33d30b3b0131690050665ec68058ce99

openstack-infra/project-config,openstack-infra/project-config