Ok thanks for clarifying. It sounds like your java app is a WAR, not a JAR, correct? Or, perhaps it's a jar, but it's a non-executable jar - it cannot be run with `java -jar my-web-app.jar`
If you create a jar that is executable as above, Cloud Foundry will just run it - so you'll get all of your custom jetty configuration. If instead, you require some other command to run this, CF will not be able to infer this, and your servlets will be run inside of a tomcat instance created by the buildpack.
If you cannot make your app an executable jar, you will have to rely on the buildpack behavior, which is non-configurable, unless you fork it.
Can you post a sanitized version of your actual app (or DM it to someone from the #release-integration channel in cloudfoundry.slack.com). Without your custom configuration we cannot really proceed.
Rob Dimsdale & Alvaro Perez-Shirley
CF Release Integration