[EAPCD] Replace use of -Xbootclasspath/p with -Xbootclasspath/a

The -Xbootclasspath/p option does not work with JDK 11 so it needs to be removed. I believe, for EAP at least, that the only reason we set -Xbootclasspath is for the logging stuff, and I've confirmed with jperkins-rhn that the still-works-with-JDK11 -Xbootclasspath/a is fine for the logging use cases. (The p vs a is prepend vs append and append is fine.)