RFR: JDK-8230974: creating rpm, get error for relative path to the license.txt

[Alexey Semenyuk]

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).

Baseline for review is [3].

[1] https://bugs.openjdk.java.net/browse/JDK-8230974

[2] http://cr.openjdk.java.net/~asemenyuk/8230974/webrev.00/

[3] http://cr.openjdk.java.net/~asemenyuk/8231280/webrev.01/