Set .root-marker variables for openstack-manuals
Set .root-marker variables for openstack-manuals

The ZUUL_* variables are only available for legacy jobs but are
required to write the root-marker file. Set the needed variables.

Change-Id: Ie6e2dbe6f1951f94c918a1aea83ad93e7b39c4b0

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