Strict matching of clusters

[mmalecki]

I've been thinking about this for some time. Consider the following situation:

conductor depends on redis. conductor and its redis instance should be co-located. So, when spawning conductor, quill could be executed like: quill configure conductor --cluster conductor --cluster eu-ams-1. If a redis instance exists in eu-ams-1, it'll be moved up, so that the first server (servers.0.redis.0) is the one from eu-ams-1. However, if no such instance exists, another instance of redis from cluster conductor will be used with no warning. This could be fixed by creating third cluster: conductor-eu-ams-1, which isn't convenient.

However, conductor depends on couchdb too. It isn't crucial for those 2 services to be co-located.

Maybe we should make this configurable?

@indexzero I'm wondering what's your opinion here.