Fix share server migration tests

This patch provides small fixes to the share server migration tests.

Change-Id: I4dcd677d53d56aad544d9a7e88b8160b704c241d
diff --git a/manila_tempest_tests/config.py b/manila_tempest_tests/config.py
index 610ae51..a24a064 100644
--- a/manila_tempest_tests/config.py
+++ b/manila_tempest_tests/config.py
@@ -262,7 +262,7 @@
                 help="Defines whether to run tests that create share from "
                      "snapshots in another pool or az. Enable this "
                      "option if the used driver supports it."),
-    cfg.BoolOpt("run_share_servers_migration_tests",
+    cfg.BoolOpt("run_share_server_migration_tests",
                 default=False,
                 help="Defines whether to run share servers migration tests. "
                      "Enable this option if the used driver supports it."),