Fix typo in documentation
Fix typo in documentation

Change-Id: If8ff20ff77e5bbe1497faee45c9ef6401b1e5921

cisco-openstack/tempest,masayukig/tempest,vedujoshi/tempest,vedujoshi/tempest,Juniper/tempest,openstack/tempest,masayukig/tempest,openstack/tempest,Juniper/tempest,cisco-openstack/tempest