veyron/runtimes/google/ipc: add options to ipc server constructor to control which endpoints to mount when publishing, and to allow for endpoint rewrite.
veyron/runtimes/google/ipc: add options to ipc server constructor to control
which endpoints to mount when publishing, and to allow for endpoint rewrite.

Details:
- the new ServerPublishOpt option is a server opt and offers the choices of
  mounting all listened endpoints (the default), or mounting the first endpoint
  only.
- the new EndpointRewriteOpt is a listener opt that tells the listener whether to
  massage the endpoint it returns to replace a tcp ip with a desired host or
  ip (this is needed for e.g. GCE where the public ip that we want to put in
  the mounttable differs from the ip that the process sees when listening).

Change-Id: I0c870399a27a9201277882abcb6a2e860a065f4c

vanadium/go.v23,vanadium/go.v23,vanadium/go.v23