Enabling registration for non-amazon datacenters on server startup.

`PeerAwareInstanceRegistry` disregards any non-amazon instances got from a peer on initial startup. This change enabled the registration.

Changes were discussed as part of pull request: https://github.com/Netflix/eureka/pull/134
Merge pull request #150 from NiteshKant/master

Enabling registration for non-amazon datacenters on server startup.