RFR: 8260592: jpackage tests fail when Desktop is not supported [v2]

[Aleksey Shipilev]

> If you run x86 configuration (cross-compiled on x86_64), then many tests would fail with:
> 
> $ CONF=linux-x86-server-fastdebug make images run-test TEST=tools/jpackage
> ...
> can not load libgnomevfs-2.so
> Exception in thread "main" java.lang.ExceptionInInitializerError
> Caused by: java.lang.UnsupportedOperationException: Desktop API is not supported on the current platform
> at java.desktop/java.awt.Desktop.getDesktop(Unknown Source)
> at com.that/com.that.main.Florence.createInstance(Unknown Source)
> at com.that/com.that.main.Florence.<clinit>(Unknown Source)
> Failed to launch JVM
> java.lang.AssertionError: Expected [0]. Actual [1]: Check command [/home/shade/trunks/jdk/build/linux-x86-server-fastdebug/test-support/jtreg_test_jdk_tools_jpackage/scratch/10/./testMainLauncherIsModular.ed4f638d/output/MainLauncherIsModularAddLauncherTest/bin/ModularAppLauncher](1) exited with 0 code
> 
> The tests probably need to check `Desktop.isDesktopSupported()`, similarly how they check `GraphicsEnvironment.isHeadless()`.
> 
> Additional testing:
>  - [x] Linux x86_32 `tools/jpackage` (now pass)
>  - [x] Linux x86_64 `tools/jpackage` (still pass)

Aleksey Shipilev has updated the pull request incrementally with two additional commits since the last revision:

 - Reinstate trace message
 - Move check higher

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2291/files
  - new: https://git.openjdk.java.net/jdk/pull/2291/files/c0975ae3..ddf28110

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2291&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2291&range=00-01

  Stats: 12 lines in 1 file changed: 6 ins; 6 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2291.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2291/head:pull/2291

PR: https://git.openjdk.java.net/jdk/pull/2291