Fix tempest compatibility

Decorator "safe_setup" was removed in Tempest project, we need to remove its
usage to fix compatibility.

Gerrit commit: https://review.openstack.org/#/c/122531/
Tempest commit: https://github.com/openstack/tempest/commit/c27feb85

Change-Id: I1c9a9a668b3d7761c07af72aff8415b86ffaa8a5
Closes-Bug: #1378677
Merge "Fix tempest compatibility"