RFR: 8220505: Allow building available installers when --installer-type not specified

[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-8220505

[2] http://cr.openjdk.java.net/~herrick/8220505/

/Andy