fix(*): all services ensure valid config file on reload

Closes #1099
Replaces #1626
test(builder): update etcd keys in builder test

The confd templates expected some more etcd keys than were seeded
before. Add those extra keys in.
fix(router): add check command for nginx config

Check for `<no value>` in nginx config, which usually means that
something is wrong with the configuration in etcd.
Merge pull request #1629 from deis/fix/check-config

fix(*): all services ensure valid config file on reload