RFR: 8272815: jpackage --type rpm produces an error: Invalid or unsupported type: [null]

[Alexey Semenyuk]

Fix jpackage error output when "--type" CLI option is missing and jpackage detects that it can't build native packages in the environment.

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Commit messages:
 - 8272815: jpackage --type rpm produces an error: Invalid or unsupported type: [null]

Changes: https://git.openjdk.java.net/jdk/pull/5512/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5512&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272815
  Stats: 18 lines in 2 files changed: 2 ins; 4 del; 12 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5512.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5512/head:pull/5512

PR: https://git.openjdk.java.net/jdk/pull/5512