Fail ISAR if any sub-thread fails

The previous method would join the first thread in threads and then block for that thread.
If that thread failed, then it would simply join the next thread, and if another thread failed,
it would do nothing.

This fixes that.

main.py

@@ -1,5 +1,6 @@
 import logging
 import os
+import time
 from logging import Logger
 from threading import Thread
 from typing import List
@@ -94,6 +95,9 @@
         thread.start()
         logger.info(f"Started thread: {thread.name}")
 
-    for thread in threads:
-        thread.join()
-        logger.info(f"Joined thread: {thread.name}")
+    while True:
+        for thread in threads:
+            if not thread.is_alive():
+                logger.critical("Thread '%s' failed - ISAR shutting down", thread.name)
+                exit(1)
+        time.sleep(state_machine.sleep_time)