Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=57049
Clarified that jvmRoute can be set using Engine.jvmRoute or a system property.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1628984 13f79535-47bb-0310-9956-ffa450edef68