test-runner: fix process cleanup loop

The processes in the list ultimately get removed for each
kill() call. This causes strange behavior since the list is
being iterated and each iteration is removing items. Instead
iterate over a new temporary list so the actual process list
can be cleaned up.

tools/test-runner

@@ -599,7 +599,7 @@ class Namespace:
 		if self.name == "root":
 			self._bus = dbus.bus.BusConnection(address_or_type=self.dbus_address)
 
-		for p in self.processes:
+		for p in list(self.processes):
 			print("Killing process %s" % p.name)
 			p.kill()