Rather than risk the heartbeat event code locking up the server control
socket, handle it in the 'idle' thread with the other work. The aim
is to remove it as a possible issue with some ongoing hangs.
(Bitbake rev: 0f9a0c7853b181817bf01863a26da21412376294)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>