hg: jdk9/sandbox/jdk: 8174694: improve error message shown when main class can't be loaded

[chris.hegarty at oracle.com]

Changeset: 96e10bc4ff66
Author:    vromero
Date:      2017-02-15 17:00 -0800
URL:       http://hg.openjdk.java.net/jdk9/sandbox/jdk/rev/96e10bc4ff66

8174694: improve error message shown when main class can't be loaded
Reviewed-by: ksrini, alanb

! src/java.base/share/classes/sun/launcher/LauncherHelper.java
! src/java.base/share/classes/sun/launcher/resources/launcher.properties
+ test/tools/launcher/MainClassCantBeLoadedTest.java