Binding on-demand #12: Log and unbind dangling TransportClients

Extracted connection in TransportClient to static class with weak
reference to TransportClient so that TransportClient is garbage
collected when left undisposed. Created finalize method that logs,
unbinds TransportClient and warns using CloseGuard.
Also adjusted some logging.

Bug: 17140907
Test: m -j RunFrameworksServicesRoboTests
Test: Manually left a dangling TransportClient and observed logs and
connections

Change-Id: I30f89e7c27579089ba29936483abd1b60c9e8e37