Backport Unity driver from Ocata (#3)

Author: Murray-LIANG

README.md

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+# Copyright (c) 2016 Dell Inc. or its subsidiaries.
+# All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+
+class StoropsException(Exception):
+    message = 'Storops Error.'
+
+
+class UnityLunNameInUseError(StoropsException):
+    pass
+
+
+class UnityResourceNotFoundError(StoropsException):
+    pass
+
+
+class UnitySnapNameInUseError(StoropsException):
+    pass
+
+
+class UnityDeleteAttachedSnapError(StoropsException):
+    pass
+
+
+class UnityResourceAlreadyAttachedError(StoropsException):
+    pass
+
+
+class UnityPolicyNameInUseError(StoropsException):
+    pass
+
+
+class UnityNothingToModifyError(StoropsException):
+    pass
+
+
+class ExtendLunError(Exception):
+    pass
+
+
+class DetachIsCalled(Exception):
+    pass
+
+
+class LunDeleteIsCalled(Exception):
+    pass
+
+
+class SnapDeleteIsCalled(Exception):
+    pass
+
+
+class UnexpectedLunDeletion(Exception):
+    pass
+
+
+class AdapterSetupError(Exception):
+    pass