RFR: JDK-8230152: No appropriate error message when wix tools missing.

[Andy Herrick]

Please review the jpackage fix for bug [1] at [2].

This is a fix for the JDK-8200758-branch branch of the open sandbox 
repository (jpackage).

[1] https://bugs.openjdk.java.net/browse/JDK-8230152

[2] http://cr.openjdk.java.net/~herrick/8230152/

Thanks

Andy,