RFR 8160359: Improve jlink logging for cases when a plugin throws exception

[Sundararajan Athijegannathan]

Please review fix for https://bugs.openjdk.java.net/browse/JDK-8160359

jdk webrev: http://cr.openjdk.java.net/~sundar/8160359/webrev.01/

top webrev: http://cr.openjdk.java.net/~sundar/8160359/top/webrev.01/

This is mainly a debugging aid for jlink invocation - in particular from
jdk makefiles. We'd like to get maximum info. like stack trace on
exception from builtin plugin invocation from jdk makefiles.

Main changes from earlier round:

* Plugin.configure should throw only IllegalArgumentException (never
PluginException)  - as suggested by Mandy earlier.

* jlink.debug turned on for JDK makefile's invocation of jlink (top
webrev) - as suggested by Claes earlier.

Earlier round of review:

http://mail.openjdk.java.net/pipermail/jigsaw-dev/2016-November/010034.html

Thanks,

-Sundar