Add wait_for_interface_detach method

The method waits for an interface to be detached from a server.
It will be used in the subsequent patch that tests tagged device
attach and detach (nova API 2.49).

Change-Id: If23bd5947dea345b30a77bc83c5b3dbfa5a4267b
diff --git a/tempest/common/waiters.py b/tempest/common/waiters.py
index 08e2a12..0e86f05 100644
--- a/tempest/common/waiters.py
+++ b/tempest/common/waiters.py
@@ -287,3 +287,24 @@
             raise lib_exc.TimeoutException(message)
 
     return body
+
+
+def wait_for_interface_detach(client, server_id, port_id):
+    """Waits for an interface to be detached from a server."""
+    body = client.list_interfaces(server_id)['interfaceAttachments']
+    ports = [iface['port_id'] for iface in body]
+    start = int(time.time())
+
+    while port_id in ports:
+        time.sleep(client.build_interval)
+        body = client.list_interfaces(server_id)['interfaceAttachments']
+        ports = [iface['port_id'] for iface in body]
+        if port_id not in ports:
+            return body
+
+        timed_out = int(time.time()) - start >= client.build_timeout
+        if timed_out:
+            message = ('Interface %s failed to detach from server %s within '
+                       'the required time (%s s)' % (port_id, server_id,
+                                                     client.build_timeout))
+            raise lib_exc.TimeoutException(message)
diff --git a/tempest/tests/common/test_waiters.py b/tempest/tests/common/test_waiters.py
index 8c62ca0..eb1e2b6 100644
--- a/tempest/tests/common/test_waiters.py
+++ b/tempest/tests/common/test_waiters.py
@@ -106,3 +106,30 @@
         self.assertRaises(lib_exc.TimeoutException,
                           waiters.wait_for_interface_status,
                           self.client, 'server_id', 'port_id', 'ACTIVE')
+
+    def _one_interface(self):
+        return {'interfaceAttachments': [{'port_id': 'port_one'}]}
+
+    def _two_interfaces(self):
+        return {'interfaceAttachments': [{'port_id': 'port_one'},
+                                         {'port_id': 'port_two'}]}
+
+    def test_wait_for_interface_detach(self):
+        self.client.list_interfaces.side_effect = [self._two_interfaces(),
+                                                   self._one_interface()]
+        with mock.patch.object(time, 'sleep') as sleep_mock:
+            start_time = int(time.time())
+            waiters.wait_for_interface_detach(self.client, 'server_id',
+                                              'port_two')
+            end_time = int(time.time())
+            self.assertLess(end_time, (start_time + self.client.build_timeout))
+            sleep_mock.assert_called_once_with(self.client.build_interval)
+
+    def test_wait_for_interface_detach_timeout(self):
+        time_mock = self.patch('time.time')
+        time_mock.side_effect = utils.generate_timeout_series(1)
+
+        self.client.list_interfaces.return_value = self._one_interface()
+        self.assertRaises(lib_exc.TimeoutException,
+                          waiters.wait_for_interface_detach,
+                          self.client, 'server_id', 'port_one')