openjdk8 doesn't build with TEST=on

[K. Macy]

It isn't obvious to a naive user how to tell it to 'run tar xzf' on jtreg4.

root at serenity:/usr/ports/java/openjdk8 # make
===>  License GPLv2 accepted by the user
===>  Found saved configuration for openjdk8-8.11.12
===>   openjdk8-8.11.12 depends on file: /usr/local/sbin/pkg - found
===> Fetching all distfiles required by openjdk8-8.11.12 for building
===>  Extracting for openjdk8-8.11.12
=> SHA256 Checksum OK for openjdk-8-src-b132-03_mar_2014.zip.
=> SHA256 Checksum OK for jtreg4.1-b08.tar.gz.
unzip: Unrecognized archive format
*** Error code 1

Stop.
make[1]: stopped in /usr/ports/java/openjdk8
*** Error code 1

Stop.
make: stopped in /usr/ports/java/openjdk8