cbauth does not work with non-localhost nodes

Calling methods that require fetching data directly from ns_server (rather than relying on the revrpc stream, such as verifyPasswordOnServer) fail when the ns_server that we are connected with is not at the "localhost" address.

This seems to be a side-effect of ns_server including "localhost" as the hostname in the URLs that it returns. A quick discussion with Timofey Barmin indicates that we should probably instead be using the address that cbauth was initialized with when sending those requests.

What is actually being implemented:
1. Special version of cbauth for external clients, which doesn't return internal passwords and resolves issues with URL's
2. Support of periodic heartbeats over REVRPC connection
3. Support of periodic heartbeats over all long lasting client/ns_server connections (streaming api's)