Eureka read/write server self registration + eureka client update.

Eureka client can now resolve eureka read cluster using discovery endpoint
on the write cluster.
This commit adds also a startup configuration mechanism for
read/write server runners.
Merge remote-tracking branch 'remotes/netflix/2.x' into tbak/2.x

Conflicts:
	eureka-core/src/main/avro/eureka-registry-model.avdl
Merge pull request #213 from tbak/2.x

Eureka read/write server self registration + eureka client update.