https://github.com/Netflix/eureka/issues/12: Added an API to update user-specific metadata.

Usage:curl -X PUT http://localhost/eureka/v2/apps/MYAPP/INSTANCE_ID/metadata?test1=test2
Merge branch 'master' of https://github.com/Netflix/eureka
https://github.com/Netflix/eureka/issues/11: Fixed a bug where Xstream deserialization was returning "null" when the appropriate type was not defined. Also, change the deserialization type check to check only for subtypes(xml or json) instead of the exact string match (for e.g.) application/xml.
Fixed a case where the region information was looked up straight from archaius instead of eureka client configuration.