RFR: 8356309: Fix issues uncovered after running jpackage tests locally with installing test packages

[Alexey Semenyuk]

Fix issues uncovered in the tests after local test runs with the installation of test packages:
 - LinuxHelper: fix a regression from [JDK-8354988](https://bugs.openjdk.org/browse/JDK-8354988). Before the [JDK-8354988](https://bugs.openjdk.org/browse/JDK-8354988) fix, when a process started with Executor didn't write to stdout, `Executor.executeAndGetFirstLineOfOutput()` returned an empty string; after the fix, it throws an exception.
 - Fix EmptyFolderTest: when an MSI is installed, it can create empty directories. Empty directories are not created only when it is unpacked. We probably never ran EmptyFolderTest in "install test packages" mode; we always executed it in "unpack test packages" mode.
 -  Fix `PackageTest.Group` to make it work correctly when a test runs jpackage to produce both exe and msi packages, and when they are installed.
 
Before the fix, the sequence was:

for (action in {create, install, uninstall}) {
  for (test in tests) {
    for (type in {exe, msi}) {
      run $action on $test of $type
    }
  }
}


After the fix, the sequence is:

for (type in {exe, msi}) {
  for (action in {create, install, uninstall}) {
    for (test in tests) {
      run $action on $test of $type
    }
  }
}


Additionally:
 - Add missing `@Test` annotation to PathGroupTest.testNullId() test case;
 - Fix typo in PListReaderTest: STRING_ARRY -> STRING_ARR**A**Y;
 - Optimize RuntimeImageTest to not run jlink if external Java runtime is supplied;
 - Add a test to RuntimeImageTest to verify jpackage strips the "jmod" directory and the "src.zip" file from an external runtime image

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

Commit messages:
 - Merge branch 'master' into local-test-followup
 - Bugfix RuntimePackageTest
 - Bugfix
 - Better test coverage
 - Add RuntimeImageTest.testStrippedFiles() test to verify jmods and src.zip files are stripped from copied runtime
 - Improve RuntimeImageTest
 - Add missing @Test annotation
 - Fix typo
 - EmptyFolderTest: bugfix
 - PackageTest: fix to make it work when exe and msi packagings are both enabled and when PackageTest.Group is used
 - ... and 5 more: https://git.openjdk.org/jdk/compare/0cb355ee...9649c077

Changes: https://git.openjdk.org/jdk/pull/24884/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24884&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8356309
  Stats: 107 lines in 7 files changed: 49 ins; 6 del; 52 mod
  Patch: https://git.openjdk.org/jdk/pull/24884.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24884/head:pull/24884

PR: https://git.openjdk.org/jdk/pull/24884