Fix NeedWantClientAuthTest for OpenJDK 13.0.2/11.0.6

[sbordet]

Jetty version
9.4.25

Java version
13.0.2/11.06

Description
OpenJDK 13.0.2 and 11.0.6 have introduced a check on CA certificates, see https://www.oracle.com/technetwork/java/javase/13-0-2-relnotes-5812268.html#JDK-8230318.

This makes the NeedWantClientAuthTest fail because the test keystore does not have the Basic Constraint CA:true in the server certificate (which is used as CA for client certificates).