Fix ping test: ping is now capable of understanding IPv6 addresses

Starting from Debian 9, ping binary can understand IPv6 addresses and
since we have more and more testnode on Debian9, test the other way
around. Maybe we should get rid of this test...

slapos/test/promise/test_is_icmp_packet_lost.py

@@ -41,18 +41,18 @@ class TestIsICMPPacketLost(unittest.TestCase):
     result = test("couscous", True, 5)
     self.assertEqual(result[4], -1)
 
-  def test_localhost6 (self):
+  def test_localhost6_with_ping6 (self):
     result = test("::1", False, 5)
     self.assertEqual(result[4], '0')
   
+  def test_localhost6_with_ping4 (self):
+    result = test("::1", True, 5)
+    self.assertEqual(result[4], '0')
+
   def test_error6(self):
     result = test("couscous", False, 5)
     self.assertEqual(result[4], -1)
 
-  def test_error_4_6(self):
-    result = test("::1", True, 5)
-    self.assertEqual(result[4], -1)
-
 if __name__ == '__main__':
   unittest.main()