Review request: JDK-8068764 java/lang/ClassLoader/ExtDirs.java failed with Exception java.lang.IllegalThreadStateException: process hasn't exited

[Mandy Chung]

http://cr.openjdk.java.net/~mchung/jdk9/webrevs/8068764/webrev.00/

The ExtDirs and EndorsedDirs tests might fail due to the insufficient wait time 
on fastdebug build on a slow machine.

This patch converts the tests to use the test library ProcessTools that will 
wait for the child process to finish or destroy it when timeout.

Mandy