dbus: Raise SIGTERM when the connection drops.

Instead of exiting directly when a client notices that the connection
got dropped, raise a SIGTERM signal to allow the client to clean up and
exit cleanly.

Bug: 26267381
Test: stop dbus. Clients exit cleanly.

Change-Id: I7e1faf1aa8b761b1b05dfde82a48882f61124acb
1 file changed