RFR: 8278205: jlink plugins should dump .class file in debug mode

[Athijegannathan Sundararajan]

jlink plugins dump .class files in debug mode. jpackage tests already set jlink.debug property to true.

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Commit messages:
 - 8278205: jlink plugins should dump .class file in debug mode

Changes: https://git.openjdk.java.net/jdk/pull/6696/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6696&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278205
  Stats: 41 lines in 5 files changed: 35 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6696.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6696/head:pull/6696

PR: https://git.openjdk.java.net/jdk/pull/6696