networking-midonet: Add networking-l2gw to PROJECTS
networking-midonet: Add networking-l2gw to PROJECTS

As a preparation to enable it for -full jobs.

Partial-Bug: #1684488
Change-Id: Iee1ec6cd7a1949da7dbe308aa0a7d75c15234df6

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