stop swallowing exceptions raised by the callback passed to run_in_bg

it is just more confusing that it is worth, especially when doing
development

subiquitycore/controller.py

@@ -49,15 +49,12 @@ class BaseController(ABC):
         """Run func() in a thread and call callback on UI thread.
 
         callback will be passed a concurrent.futures.Future containing
-        the result of func(). The result of callback is discarded. Any
-        exception will be logged.
+        the result of func(). The result of callback is discarded. An
+        exception will crash the process so be careful!
         """
         fut = self.pool.submit(func)
         def in_main_thread(ignored):
-            try:
-                callback(fut)
-            except:
-                log.exception("callback %s after calling %s failed", callback, func)
+            callback(fut)
         pipe = self.loop.watch_pipe(in_main_thread)
         def in_random_thread(ignored):
             os.write(pipe, b'x')