Volume reset to maintenance mode

Update existing test with reset-volume state to maintenance.

The purpose here is to verify that cinder state can be changed to maintenance.

Here are all valid states for cinder:
https://docs.openstack.org/developer/cinder/api/cinder.api.contrib.admin_actions.html

Change-Id: I5226b000317b2a9ab034afa90c3461011db4a030
diff --git a/tempest/api/volume/admin/test_volumes_actions.py b/tempest/api/volume/admin/test_volumes_actions.py
index 02b10f9..990900b 100644
--- a/tempest/api/volume/admin/test_volumes_actions.py
+++ b/tempest/api/volume/admin/test_volumes_actions.py
@@ -32,7 +32,9 @@
     def test_volume_reset_status(self):
         # test volume reset status : available->error->available
         volume = self.create_volume()
-        for status in ['error', 'available']:
+        self.addCleanup(self.admin_volume_client.reset_volume_status,
+                        volume['id'], status='available')
+        for status in ['error', 'available', 'maintenance']:
             self.admin_volume_client.reset_volume_status(
                 volume['id'], status=status)
             volume_get = self.admin_volume_client.show_volume(