Move wait_for_interface_status from service client

wait_for_interface_status is used in test_attach_interfaces only
and the method is just a wrapper of sevice client method.
The service client module is not right place for the method.
Then this patch migrate the method to test_attach_interfaces.

Partially implements blueprint consistent-service-method-names

Change-Id: Ie6c05c83c6f029036f0ba105b6cdb82208616f38
diff --git a/tempest/api/compute/servers/test_attach_interfaces.py b/tempest/api/compute/servers/test_attach_interfaces.py
index c3c50d6..396327b 100644
--- a/tempest/api/compute/servers/test_attach_interfaces.py
+++ b/tempest/api/compute/servers/test_attach_interfaces.py
@@ -46,6 +46,28 @@
         super(AttachInterfacesTestJSON, cls).setup_clients()
         cls.client = cls.os.interfaces_client
 
+    def wait_for_interface_status(self, server, port_id, status):
+        """Waits for a interface to reach a given status."""
+        body = self.client.show_interface(server, port_id)
+        interface_status = body['port_state']
+        start = int(time.time())
+
+        while(interface_status != status):
+            time.sleep(self.build_interval)
+            body = self.client.show_interface(server, port_id)
+            interface_status = body['port_state']
+
+            timed_out = int(time.time()) - start >= self.build_timeout
+
+            if interface_status != status and timed_out:
+                message = ('Interface %s failed to reach %s status '
+                           '(current %s) within the required time (%s s).' %
+                           (port_id, status, interface_status,
+                            self.build_timeout))
+                raise exceptions.TimeoutException(message)
+
+        return body
+
     def _check_interface(self, iface, port_id=None, network_id=None,
                          fixed_ip=None, mac_addr=None):
         self.assertIn('port_state', iface)
@@ -61,14 +83,14 @@
     def _create_server_get_interfaces(self):
         server = self.create_test_server(wait_until='ACTIVE')
         ifs = self.client.list_interfaces(server['id'])
-        body = self.client.wait_for_interface_status(
+        body = self.wait_for_interface_status(
             server['id'], ifs[0]['port_id'], 'ACTIVE')
         ifs[0]['port_state'] = body['port_state']
         return server, ifs
 
     def _test_create_interface(self, server):
         iface = self.client.create_interface(server['id'])
-        iface = self.client.wait_for_interface_status(
+        iface = self.wait_for_interface_status(
             server['id'], iface['port_id'], 'ACTIVE')
         self._check_interface(iface)
         return iface
@@ -77,7 +99,7 @@
         network_id = ifs[0]['net_id']
         iface = self.client.create_interface(server['id'],
                                              network_id=network_id)
-        iface = self.client.wait_for_interface_status(
+        iface = self.wait_for_interface_status(
             server['id'], iface['port_id'], 'ACTIVE')
         self._check_interface(iface, network_id=network_id)
         return iface
diff --git a/tempest/services/compute/json/interfaces_client.py b/tempest/services/compute/json/interfaces_client.py
index 9d6c9d4..0e0ff47 100644
--- a/tempest/services/compute/json/interfaces_client.py
+++ b/tempest/services/compute/json/interfaces_client.py
@@ -14,12 +14,10 @@
 #    under the License.
 
 import json
-import time
 
 from tempest.api_schema.response.compute.v2_1 import interfaces as schema
 from tempest.api_schema.response.compute.v2_1 import servers as servers_schema
 from tempest.common import service_client
-from tempest import exceptions
 
 
 class InterfacesClient(service_client.ServiceClient):
@@ -60,28 +58,6 @@
         self.validate_response(schema.delete_interface, resp, body)
         return service_client.ResponseBody(resp, body)
 
-    def wait_for_interface_status(self, server, port_id, status):
-        """Waits for a interface to reach a given status."""
-        body = self.show_interface(server, port_id)
-        interface_status = body['port_state']
-        start = int(time.time())
-
-        while(interface_status != status):
-            time.sleep(self.build_interval)
-            body = self.show_interface(server, port_id)
-            interface_status = body['port_state']
-
-            timed_out = int(time.time()) - start >= self.build_timeout
-
-            if interface_status != status and timed_out:
-                message = ('Interface %s failed to reach %s status '
-                           '(current %s) within the required time (%s s).' %
-                           (port_id, status, interface_status,
-                            self.build_timeout))
-                raise exceptions.TimeoutException(message)
-
-        return body
-
     def add_fixed_ip(self, server_id, network_id):
         """Add a fixed IP to input server instance."""
         post_body = json.dumps({