Changed ConnectToService to accept error callback

Method is async and can return error with delay.

BUG: 24267885
Change-Id: I5a8d15d2cc7872bee4e54033bac36f1b839c5559
Reviewed-on: https://weave-review.googlesource.com/1114
Reviewed-by: Alex Vakulenko <avakulenko@google.com>