Print something to Docker logs when service is dead

No output in Docker logs makes all log readers stuck in a read() call.
Printing garbage lines allows for non-asyncio timeouts to kick in.

Signed-off-by: Vitaliy Potyarkin <v.potyarkin@yadro.com>

src/frostfs_testlib/component_tests/container.py

@@ -44,7 +44,7 @@ class ContainerizedService:
         if self._testcontainer is None:
             self.create()
         self.stop()
-        self._pid1(f"{{ {self.command} ; }} &")
+        self._pid1(f"{{ {self.command}; while sleep 1; do echo Service died.; done; }} &")
 
     def stop(self):
         self._pid1(