Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=55521
Ensure that session.expire() doesn't return until the session has been invalidated.
Ensure that the return valid of session.isValid() is consistent the current state.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1520349 13f79535-47bb-0310-9956-ffa450edef68