convert unicode to string before we connect to rados

rados client only support string argument, therefore we have to
convert argument to string first.

closes-Bug: #1672792

Change-Id: I007c15dc61db9dbf7df7b8bea7c3dce49f0396f5
(cherry picked from commit 2f5ebdba5f)

nova/tests/unit/virt/libvirt/storage/test_rbd.py

@@ -310,6 +310,12 @@ class RbdTestCase(test.NoDBTestCase):
         mock_rados.Rados.open_ioctx.assert_called_once_with(self.rbd_pool)
         mock_rados.Rados.shutdown.assert_called_once_with()
 
+    @mock.patch.object(rbd_utils, 'rados')
+    def test_connect_to_rados_unicode_arg(self, mock_rados):
+        self.driver._connect_to_rados(u'unicode_pool')
+        self.mock_rados.Rados.open_ioctx.assert_called_with(
+            test.MatchType(str))
+
     def test_ceph_args_none(self):
         self.driver.rbd_user = None
         self.driver.ceph_conf = None

nova/virt/libvirt/storage/rbd_utils.py

@@ -135,7 +135,11 @@ class RBDDriver(object):
         try:
             client.connect()
             pool_to_open = pool or self.pool
-            ioctx = client.open_ioctx(pool_to_open)
+            # NOTE(luogangyi): open_ioctx >= 10.1.0 could handle unicode
+            # arguments perfectly as part of Python 3 support.
+            # Therefore, when we turn to Python 3, it's safe to remove
+            # str() conversion.
+            ioctx = client.open_ioctx(str(pool_to_open))
             return client, ioctx
         except rados.Error:
             # shutdown cannot raise an exception