I don't know if you have finally got the solution. If not, then you have to
a) worker.loadbalancer.sticky_session=1 in conf/workers.properties
b) add jvmRoute attribute to server.xml
But for all of this to work, you should have used "all" server type and not "default" server type if I am not wrong.
The default server it's not for clustering, use the "all" configuration