Assert contents of returned devices in test

Having this test fail with:

testtools.matchers._impl.MismatchError: 2 != 4

Doesn't really tell the developer what went wrong.
We can just compare the lists of devices directly so a mismatch
will show the devices that leaked in.

TrivialFix

Change-Id: Ic5a3b347bea7e5aa8a5caee5035568e5954f58dc
(cherry picked from commit 63ff8f7fbe)

neutron/tests/functional/agent/linux/test_dhcp.py

@@ -77,7 +77,8 @@ class TestDhcp(functional_base.BaseSudoTestCase):
         ipw = ip_lib.IPWrapper(namespace="qdhcp-foo_id")
         devices = ipw.get_devices(exclude_loopback=True)
         self.addCleanup(ipw.netns.delete, 'qdhcp-foo_id')
-        self.assertEqual(2, len(devices))
+        self.assertEqual(sorted(["tapfoo_id2", "tapfoo_id3"]),
+                         sorted(map(str, devices)))
         # setting up dhcp for the network
         dev_mgr.setup(tests_base.AttributeDict(network))
         common_utils.wait_until_true(