Replace a few invocations of control_event_bootstrap() with calls from
the bootstrap tracker subsystem. This mostly leaves behavior
unchanged. The actual behavior changes come in the next commit.
Part of ticket 27167.
Add a tracker for bootstrap progress, tracking events related to
origin circuit and ORCONN states. This uses the ocirc_event and
orconn_event publish-subscribe subsystems.
Part of ticket 27167.