Fix typo. Doesn't change test but reduces confusion.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1645536 13f79535-47bb-0310-9956-ffa450edef68
In order to enable define in Cluster element, ClusterSingleSignOn implements ClusterValve.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1645595 13f79535-47bb-0310-9956-ffa450edef68