RFR: 8260592: jpackage tests fail when Desktop is not supported

[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)

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

Commit messages:
 - 8260592: jpackage tests fail when Desktop is not supported

Changes: https://git.openjdk.java.net/jdk/pull/2291/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2291&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8260592
  Stats: 6 lines in 1 file changed: 6 ins; 0 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