Request exclusive access when crashing via fatal()

Request exclusive access when crashing via fatal()

When loading the configuration fails, there might be already other tasks
running and calling OpenSSL library functions.  The OpenSSL on_exit
handler is called when exiting the main process and there's a timing
race between the on_exit function that destroys OpenSSL allocated
resources (threads, locks, ...) and other tasks accessing the very same
resources leading to a crash in the system threading library. Therefore,
the fatal() function needs to request exlusive access to the task
manager to finish the already running tasks and exit only when no other
tasks are running.