Add Share Migration tempest functional tests

This patch adds functional tests for Share Migration,
running on generic driver DHSS = true mode.

Implements: blueprint share-migration
Change-Id: I64b0a3ee77b27278cc294f72702408a27888e0e9
diff --git a/manila_tempest_tests/share_exceptions.py b/manila_tempest_tests/share_exceptions.py
index 0f3de85..33478cd 100644
--- a/manila_tempest_tests/share_exceptions.py
+++ b/manila_tempest_tests/share_exceptions.py
@@ -48,5 +48,10 @@
     message = "Provided invalid resource: %(message)s"
 
 
+class ShareMigrationException(exceptions.TempestException):
+    message = ("Share %(share_id)s failed to migrate from "
+               "host %(src)s to host %(dest)s.")
+
+
 class ResourceReleaseFailed(exceptions.TempestException):
     message = "Failed to release resource '%(res_type)s' with id '%(res_id)s'."