Support setting class_path and class name.

This PR enhances the java driver to allow setting the class path and
class name to run. It also fixes an issue that would make the Java
driver attempt to chroot regardless of operating system (this never
effected a released version of Nomad).

client/driver/test-resources/java/Hello.java

@@ -0,0 +1,12 @@
+public class Hello {
+	public static void main(String[] args) {
+		while (true) {
+			System.out.println("Hello");
+			try {
+				Thread.sleep(1000); //1000 milliseconds is one second.
+			} catch(InterruptedException ex) {
+				Thread.currentThread().interrupt();
+			}
+		}
+	}
+}