bug(systemd): fix dependencies

This commit does several things:
* Refactor After and Requires to list all units on one line
* Make seed-registry job dependent upon deis-registry
* Make controller dependent on (and wait for) Builder
* Make all services only start after etcd

closes #706, #708
Merge pull request #718 from opdemand/carmstrong/systemd_depenencies

bug(systemd): fix dependencies