ext/pci: handle 'qubes-close' event

Move cache cleanup to 'qubes-close' event handler, instead of doing it
specifically in tests.

qubes/ext/pci.py

@@ -313,6 +313,12 @@ class PCIDeviceExtension(qubes.ext.Extension):
             else:
                 raise
 
+    @qubes.ext.handler('qubes-close', system=True)
+    def on_app_close(self, app, event):
+        # pylint: disable=unused-argument,no-self-use
+        _cache_get.cache_clear()
+
+
 @functools.lru_cache(maxsize=None)
 def _cache_get(vm, ident):
     ''' Caching wrapper around `PCIDevice(vm, ident)`. '''

qubes/tests/__init__.py

@@ -410,7 +410,6 @@ class QubesTestCase(unittest.TestCase):
         self.loop = asyncio.get_event_loop()
         self.addCleanup(self.cleanup_loop)
         self.addCleanup(self.cleanup_traceback)
-        self.addCleanup(qubes.ext.pci._cache_get.cache_clear)
 
     def cleanup_traceback(self):
         '''Remove local variables reference from tracebacks to allow garbage