Ignore errorcode=4 when executing cryptsetup remove command

If an attached encrypted volume is failed to detach from the instance
when deleting that instance, user can not delete that instance at all.

This patch adds 4 in check_exit_code when executing `cryptsetup remove`
command to eat that exception.

PS: exit_code = 4 indicate ENODEV error which means no device(also includes
the crypt device inactive).

Closes-Bug: #1482066
Change-Id: I12e2a52068850528a4bd68486344b74eb9b82c88

nova/tests/unit/volume/encryptors/test_cryptsetup.py

@@ -78,7 +78,7 @@ class CryptsetupEncryptorTestCase(test_base.VolumeEncryptorTestCase):
 
         mock_execute.assert_has_calls([
             mock.call('cryptsetup', 'remove', self.dev_name,
-                      run_as_root=True, check_exit_code=True),
+                      run_as_root=True, check_exit_code=[0, 4]),
         ])
         self.assertEqual(1, mock_execute.call_count)
 
@@ -88,7 +88,7 @@ class CryptsetupEncryptorTestCase(test_base.VolumeEncryptorTestCase):
 
         mock_execute.assert_has_calls([
             mock.call('cryptsetup', 'remove', self.dev_name,
-                      run_as_root=True, check_exit_code=True),
+                      run_as_root=True, check_exit_code=[0, 4]),
         ])
         self.assertEqual(1, mock_execute.call_count)
 

nova/volume/encryptors/cryptsetup.py

@@ -103,8 +103,11 @@ class CryptsetupEncryptor(base.VolumeEncryptor):
     def _close_volume(self, **kwargs):
         """Closes the device (effectively removes the dm-crypt mapping)."""
         LOG.debug("closing encrypted volume %s", self.dev_path)
+        # cryptsetup returns 4 when attempting to destroy a non-active
+        # dm-crypt device. We are going to ignore this error code to make
+        # nova deleting that instance successfully.
         utils.execute('cryptsetup', 'remove', self.dev_name,
-                      run_as_root=True, check_exit_code=True)
+                      run_as_root=True, check_exit_code=[0, 4])
 
     def detach_volume(self, **kwargs):
         """Removes the dm-crypt mapping for the device."""