Prevent the SSO deregister when web application is stopped or reloaded.
When StandardManager(pathname="") or DeltaManager stops normally, all sessions in the context are expired.
In this case, because most sessions is not time-out, SSO deregister was triggered.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1439757 13f79535-47bb-0310-9956-ffa450edef68