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/tests/api/base.py b/manila_tempest_tests/tests/api/base.py
index 554ba35..6444ccc 100644
--- a/manila_tempest_tests/tests/api/base.py
+++ b/manila_tempest_tests/tests/api/base.py
@@ -304,6 +304,13 @@
         return share
 
     @classmethod
+    def migrate_share(cls, share_id, dest_host, client=None):
+        client = client or cls.shares_client
+        client.migrate_share(share_id, dest_host)
+        share = client.wait_for_migration_completed(share_id, dest_host)
+        return share
+
+    @classmethod
     def create_share(cls, *args, **kwargs):
         """Create one share and wait for available state. Retry if allowed."""
         result = cls.create_shares([{"args": args, "kwargs": kwargs}])