Stop allowing install_users for zuul workers
Stop allowing install_users for zuul workers

Rooters' keyste are now managed with configdrive and we don't want to
have to manage users with puppet any more, so let's clean up this code.

Change-Id: Ifcca38a0754e4a76d36c4819e3fd7370256ade71

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