java/net/httpclient/security/Driver.java in JDK 9. It needs a cmd line option
to add the httpclient incubator module explicitly to the sub command launcher

diff -r 949799faf431 test/java/net/httpclient/security/Driver.java
--- a/test/java/net/httpclient/security/Driver.java Thu Feb 02 10:28:47 2017 +0100
+++ b/test/java/net/httpclient/security/Driver.java Fri Feb 10 09:21:34 2017 +0000
@@ -127,6 +127,7 @@
             cmd.add("-Dtest.src=" + testSrc);
             cmd.add("-Dtest.classes=" + testClasses);
             cmd.add("-Djava.security.manager");
+ cmd.add("--add-modules=jdk.incubator.httpclient");
             cmd.add("-Djava.security.policy=" + testSrc + sep + policy);
             cmd.add("-Dport.number=" + Integer.toString(Utils.getFreePort()));
             cmd.add("-Dport.number1=" + Integer.toString(Utils.getFreePort()));