JDK9 removes support for sun.boot.class.path

Cite from: http://openjdk.java.net/jeps/261

_Removed: Bootstrap class-path options

In earlier releases the -Xbootclasspath option allows the default bootstrap class path to be overridden, and the -Xbootclasspath/p option allows a sequence of files and directories to be prepended to the default path. The computed value of this path is reported via the JDK-specific system property sun.boot.class.path.

With the module system in place there is no longer a bootstrap class path as such, so the javac compiler only supports the -Xbootclasspath option in legacy mode, the java launcher no longer supports either option, and the system property sun.boot.class.path will be removed._