Fix rekeying volume with legacy encryption provider

Update volume_utils.check_encryption_provider() so it translates
a legacy provider class in the encryption dict it returns. For
example, if the volume's encryption metadata specifies
"nova.volume.encryptors.luks.LuksEncryptor" for the provider,
the function will a dict with "luks" as the provider.

Closes-Bug: #1886689
Change-Id: I172dab1641207849fdd6a9848ac7573cba236a8b

cinder/tests/unit/test_volume_utils.py

@@ -1188,6 +1188,7 @@ def test_check_encryption_provider(self, encryption_metadata):
                 volume,
                 mock.sentinel.context)
             self.assertEqual('aes-xts-plain64', ret['cipher'])
+            self.assertEqual('luks', ret['provider'])
 
     def test_check_encryption_provider_invalid(self):
         encryption_metadata = {'cipher': 'aes-xts-plain64',

cinder/volume/volume_utils.py

@@ -1202,6 +1202,7 @@ def check_encryption_provider(db, volume, context):
     provider = encryption['provider']
     if provider in encryptors.LEGACY_PROVIDER_CLASS_TO_FORMAT_MAP:
         provider = encryptors.LEGACY_PROVIDER_CLASS_TO_FORMAT_MAP[provider]
+        encryption['provider'] = provider
     if provider != encryptors.LUKS:
         message = _("Provider %s not supported.") % provider
         raise exception.VolumeDriverException(message=message)