Cleanup .zuul.yaml
Cleanup .zuul.yaml

Some cleanups and improvements:
* Add required-projects to py36 job
* Use openstack-lower-constraints template instead of individual jobs
* Sort list of templates

Change-Id: I2ccb71b14a9118e64a5a5b81a30a4bab550caf62

openstack/zaqar-ui,openstack/zaqar-ui,openstack/zaqar-ui,openstack/zaqar-ui