Fix: report initialization error of app registration thread

The health check tests use the testpoints() in the application
registration thread to force a pthread_exit() or simulate a
catastrophic error within the thread.

The testpoints were moved before the signal that the thread's
initialization was completed by recent changes. This caused the thread
to fail to complete its initialization, causing a deadlock of the
session daemon on launch.

This commit reports initialization errors through the
launch_application_registration_thread() function to the "main" thread
and shuts down the session daemon. It also moves the testpoints after
the thread's initialization to respect the test's intent.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>