Back-port r1628984 to fix https://issues.apache.org/bugzilla/show_bug.cgi?id=57049
Clarify that jvmRoute can be set with either Engine.jvmRoute or a system property.


git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1628985 13f79535-47bb-0310-9956-ffa450edef68