Add tests for share server migration

This patch adds new positive and negative tests for
share server migration.

Partially-implements: bp share-server-migration
Co-Authored-By: Daniel Tapia <danielarthurt@gmail.com>

Change-Id: Ice973bd2ad15bfb432e51da595b53c0480adba14
Depends-On: Ic0751027d2c3f1ef7ab0f7836baff3070a230cfd
Depends-On: I46a0cee0a4625d950f02fa7a5bf612de926451b5
Depends-On: I813801fd64d4d605c0a4fe06c7a130ad00865b6d
diff --git a/manila_tempest_tests/share_exceptions.py b/manila_tempest_tests/share_exceptions.py
index 67b4fca..9466afe 100644
--- a/manila_tempest_tests/share_exceptions.py
+++ b/manila_tempest_tests/share_exceptions.py
@@ -80,3 +80,8 @@
 class ShareServerBuildErrorException(exceptions.TempestException):
     message = ("Share server %(server_id)s failed to build and is in ERROR "
                "status")
+
+
+class ShareServerMigrationException(exceptions.TempestException):
+    message = ("Share server %(server_id)s failed to migrate and is in ERROR "
+               "status")