Working on channels (WIP)
Merge pull request #186 from tbak/2.x

Add DataCenterInfo and a few other abstraction
Merge branch '2.x' of https://github.com/Netflix/eureka into 2.x-channels

Conflicts:
	eureka-core/src/main/java/com/netflix/eureka/registry/InstanceInfoField.java
	eureka-core/src/main/java/com/netflix/eureka/transport/EurekaTransports.java
	eureka-server/src/main/java/com/netflix/eureka/server/transport/tcp/registration/AvroRegistrationModule.java
	eureka-server/src/main/java/com/netflix/eureka/server/transport/tcp/registration/JsonRegistrationModule.java
WIP
Fix failing tests.
Channel/transport updates - WIP
Reimplement MessageBroker acknowledgement timeout mechanism.
Get rid of acknowledgement correlation id.