test: infamy: Add optional test cleanup

If a test need to clean up itself disregarding test status,
it can add an optional test-cleanup phase.

This is useful if the test in some circomstances leave the device in a
bad state. This can be used to restore the unit to its ordinary state.

test/infamy/tap.py

@@ -13,8 +13,17 @@ def __init__(self, output=sys.stdout):
         if self.out == sys.stdout:
             sys.stdout = self.commenter
 
+        self.test_cleanup=[]
         self.steps = 0
 
+    def set_test_cleanup(self, fn):
+        self.test_cleanup.append(fn)
+
+    def cleanup(self):
+        infamy.netns.IsolatedMacVlans.Cleanup()
+        for test_cleanup in reversed(self.test_cleanup):
+            test_cleanup()
+
     def __enter__(self):
         now = datetime.datetime.now().strftime("%F %T")
         self.out.write(f"# Starting ({now})\n")
@@ -26,7 +35,7 @@ def __exit__(self, _, e, __):
         self.out.write(f"# Exiting ({now})\n")
         self.out.flush()
 
-        infamy.netns.IsolatedMacVlans.Cleanup()
+        self.cleanup()
 
         if not e:
             self._not_ok("Missing explicit test result\n")