fix(controller/scheduler): only announce 'web' and 'cmd' processes

Currently the nginx routers gets announced all types of processes.
This causes problems as both non-web and web processes are mixed
together by the router. The router should only be serving 'web'
processes for buildpacks or 'cmd' processes for dockerfiles.

This fix stops announcing any processes that does not have '.web'
or '.cmd'.

TODO: test coverage missing.

closes #1256
this can be further optimized (if my syntax-fu is correct):

```
if command in ['web', 'cmd', '']:
```

Also I'm not sure we want to allow null commands, since this was never used in the platform anyways. See https://github.com/deis/deis/pull/1041