Remove all uses of assignment expressions.

This is needed to port to Python 3.7 because
Raspbian 10 doesn't have Python 3.8.

Signed-off-by: Oleg Girko <ol@infoserver.lv>

kvmd/aiotools.py

@@ -177,5 +177,6 @@ async def run_region_task(
 
     if entered.done():
         return
-    if (exc := task.exception()) is not None:
+    exc = task.exception()
+    if exc is not None:
         raise exc