python/machine: Handle termination cases without QMP

If we request a shutdown of a VM without a QMP console, we'll just hang
waiting. Not ideal.

Add in code that attempts graceful termination in these cases.  Tested
lightly; it appears to work and I doubt we rely on this case anywhere,
but it's a corner you're allowed to wedge yourself in, so it should be
handled.

Signed-off-by: John Snow <jsnow@redhat.com>

python/qemu/machine/machine.py

@@ -547,6 +547,12 @@ def _soft_shutdown(self, timeout: Optional[int]) -> None:
             finally:
                 # Regardless, we want to quiesce the connection.
                 self._close_qmp_connection()
+        elif not self._quit_issued:
+            LOG.debug(
+                "Not anticipating QEMU quit and no QMP connection present, "
+                "issuing SIGTERM"
+            )
+            self._subp.terminate()
 
         # May raise subprocess.TimeoutExpired
         LOG.debug(