Use assertIn and assertNotIn

Use assertIn and assertNotIn

Neutron tests should use:

  self.assertIn(value, list)
  self.assertNotIn(value, list)

instead of:

  self.assertTrue(value in list)
  self.assertFalse(value in list)

because assertIn and assertNotIn raise more meaningful errors:

  self.assertIn(3, [1, 2]
  >>> MismatchError: 3 not in [1, 2]

  self.assertTrue(3 in [1, 2])
  >>> AssertionError: False is not true

Closes-Bug: #1218713

Change-Id: Ic8492a88935bf005feb9dae726a4bee604a8bd09