RFR: JDK-8139969 Fix unzip in compare.sh broken by JDK-8136813

[Magnus Ihse Bursie]

Unfortunately the logging of compare.sh introduced in JDK-8136813 broke 
unzip.

In JDK-8136813 we started exportin the shell variable UNZIP, which 
contains the path to UNZIP. Unfortunately, UNZIP is interpreted by UNZIP 
as a variable containing extra options to add to the command line.

Bug: https://bugs.openjdk.java.net/browse/JDK-8139969
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8139969-fix-unzip-in-compare/webrev.01

/Magnus