RFR 8171380: Remove exports from jdk.jlink

[Chris Hegarty]

The Jlink Plugin API is not going to be supported in 9, so
should not be exported [1], for use by third parties. Besides
the removal of the export, most of the changes are adding
@modules tags to existing tests.

http://cr.openjdk.java.net/~chegar/8171380.00/

Note: Sundar will follow up with 8172864 [2] to remove the
'--plugin-module-path'. Custom plugins can be written and
deployed on the class path using the --add-exports command
line, if required.

This change depends on fix in jtreg b05 [3], so bumps the
minimum required version.

-Chris.

[1] https://bugs.openjdk.java.net/browse/JDK-8171380
[2] https://bugs.openjdk.java.net/browse/JDK-8172864
[3] http://hg.openjdk.java.net/code-tools/jtreg/rev/f79ef1ecc483