Close connection to ceph after cinder bakcup

If we don't close connection to ceph cluster,
The connection count increases with cinder bakcup until exceed max open files.
Then rise OSError: [Errno 24] Too many open files

This patch is to close connection to ceph cluster after cinder backup.

Change-Id: I2fb243d2a57771dc3589e96db54e998e2c1c8ef7
Closes-bug: #1628626

os_brick/initiator/linuxrbd.py

@@ -112,15 +112,18 @@ class RBDVolume(object):
 
         self.client = client
 
-    def __enter__(self):
-        return self
-
-    def __exit__(self, type_, value, traceback):
+    def close(self):
         try:
             self.image.close()
         finally:
             self.client.disconnect()
 
+    def __enter__(self):
+        return self
+
+    def __exit__(self, type_, value, traceback):
+        self.close()
+
     def __getattr__(self, attrib):
         return getattr(self.image, attrib)
 
@@ -229,4 +232,4 @@ class RBDVolumeIOWrapper(io.RawIOBase):
     # in this case is unwanted since the rbd image may have been closed prior
     # to the autoclean - currently triggering a segfault in librbd.
     def close(self):
-        pass
+        self.rbd_image.close()

os_brick/tests/initiator/test_linuxrbd.py

@@ -146,5 +146,13 @@ class RBDVolumeIOWrapperTestCase(base.TestCase):
     def test_fileno(self):
         self.assertRaises(IOError, self.mock_volume_wrapper.fileno)
 
-    def test_close(self):
-        self.mock_volume_wrapper.close()
+    @mock.patch('os_brick.initiator.linuxrbd.rbd')
+    @mock.patch('os_brick.initiator.linuxrbd.rados')
+    @mock.patch.object(linuxrbd.RBDClient, 'disconnect')
+    def test_close(self, rbd_disconnect, mock_rados, mock_rbd):
+        rbd_client = linuxrbd.RBDClient('user', 'pool')
+        rbd_volume = linuxrbd.RBDVolume(rbd_client, 'volume')
+        rbd_handle = linuxrbd.RBDVolumeIOWrapper(
+            linuxrbd.RBDImageMetadata(rbd_volume, 'pool', 'user', None))
+        rbd_handle.close()
+        self.assertEqual(1, rbd_disconnect.call_count)