RFR: 8279995: jpackage --add-launcher option should allow overriding description

[Alexander Matveev]

Added ability to override description for additional launchers via "description" property.

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Commit messages:
 - 8279995: jpackage --add-launcher option should allow overriding description

Changes: https://git.openjdk.java.net/jdk/pull/7399/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7399&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8279995
  Stats: 18 lines in 5 files changed: 8 ins; 0 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7399.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7399/head:pull/7399

PR: https://git.openjdk.java.net/jdk/pull/7399