Improve test coverage for share migration

- Added tests to validate the migration functionality
for a replicated share.
- Added tests to validate the extend and shrink
functionality on migrated share.
- Added tests to cover the preserve snapshot
functionality on migrated share.
- Current waiter logic in migration_progress
method of dummy driver causes every migration
test to take over 4 minutes to complete.
Therefore, updated the method to cut the
overall time in half and avoid the possible timeout.

Partially-Implements: bp ocata-migration-improvements
Change-Id: Ia7c7eb7b48b464aa670073e8c0795369bd972678
diff --git a/manila_tempest_tests/config.py b/manila_tempest_tests/config.py
index ee3dd42..0f9cc69 100644
--- a/manila_tempest_tests/config.py
+++ b/manila_tempest_tests/config.py
@@ -192,6 +192,10 @@
                 deprecated_name="run_migration_tests",
                 default=False,
                 help="Enable or disable driver-assisted migration tests."),
+    cfg.BoolOpt("run_migration_with_preserve_snapshots_tests",
+                default=False,
+                help="Enable or disable migration with "
+                     "preserve_snapshots tests set to True."),
     cfg.BoolOpt("run_manage_unmanage_tests",
                 default=False,
                 help="Defines whether to run manage/unmanage tests or not. "