Fix CVE-2011-2204.

      Prevent user passwords appearing in log files if a runtime exception (e.g. OOME) occurs while creating a new user for a MemoryUserDatabase via JMX.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1140070 13f79535-47bb-0310-9956-ffa450edef68