Cortex single-process (lite) mode.

[tomwilkie]

A small bit of refactoring was needed:

• Don't try and read eth0 ip address on startup and then fail.
• Expose a flag for an in memory ring KV store, and change the naming of this interface in preparation for etcd support.
• Add a flag to do non-multitenant (inject userid 0 on every request)
• Merge all schema-relate config into a single struct, and stop embedding it.

[tomwilkie]

@jml you mentioned you were interested in this?

[jml]

Interested, yes. Unfortunately not enough to be able to give it the review that it deserves.

[jml]

Thanks!