Consider chronos*.yaml for deploy checks (Closes: #110)

[nhandler]

This will avoid paasta check message such as:

✗ There are some instance(s) in deploy.yaml that are not referenced
  by any marathon instance:
  cluster-name.batch-name, cluster-name2.batch-name
  You should probably delete these deploy.yaml entries if they are unused.

when there is a chronos-*.yaml file referencing the instance.

This change also will not show:

✗ No marathon.yaml exists, so your service cannot be deployed.
  Push a marathon-[superregion].yaml and run `paasta generate-pipeline`.
  More info: http://y/yelpsoa-configs

if a chronos.yaml file exists (and will show a more accurate message if neither yaml file exists).

Closes #110

[solarkennedy]

ship