Retry waiting for javac under Vulpix

[som-snytt]

If running a single test, the pool shutdown
is likely to subvert waitFor the javac process.
Catch the InterruptedException and try again
with a timed wait of generous but finite duration,
to accommodate testing by developers. This quick
fix does not correct the race, which presumably
does not matter because of the order in which tests
are ordinarily submitted.

For example, tests/pos-java-interop/t2940:

sbt:scala3> testCompilation t2940
[snip]
[info] Test dotty.tools.dotc.CompilationTests.posTwice started
[                                        ] completed (0/1, 0 failed, 2s)java.lang.InterruptedException
        at java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1640)compiler / Test / testOnly 3s
        at java.base/java.lang.ProcessImpl.waitFor(ProcessImpl.java:447)
[snip]
java.util.concurrent.ExecutionException: java.lang.InterruptedException
        at java.base/java.util.concurrent.ForkJoinTask.reportExecutionException(ForkJoinTask.java:581)
        at java.base/java.util.concurrent.ForkJoinTask.get(ForkJoinTask.java:993)
        at dotty.tools.vulpix.ParallelTesting.dotty$tools$vulpix$ParallelTesting$Test$$_$executeTestSuite$$anonfun$4(ParallelTesting.scala:687)
[snip long stack trace]

[som-snytt]

Locally, I just saw a couple of interrupted tests while scala3-bootstrapped/test.

[info] Test dotty.tools.dotc.BootstrappedOnlyCompilationTests.posMacros started
[======================================> ] completed (327/328, 0 failed, 21s)java.lang.InterruptedException
        at java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1722)
        at java.base/java.lang.ProcessImpl.waitFor(ProcessImpl.java:447)
        at dotty.tools.vulpix.ParallelTesting$Test.compileWithOtherCompiler(ParallelTesting.scala:628)
        at dotty.tools.vulpix.ParallelTesting$CompilationLogic.compileTestSource$$anonfun$1$$anonfun$1(ParallelTesting.scala:238)
        at scala.collection.immutable.List.map(List.scala:246)
        at dotty.tools.vulpix.ParallelTesting$CompilationLogic.compileTestSource$$anonfun$1(ParallelTesting.scala:238)
        at scala.util.Try$.apply(Try.scala:210)
        at dotty.tools.vulpix.ParallelTesting$CompilationLogic.dotty$tools$vulpix$ParallelTesting$CompilationLogic$$compileTestSource(ParallelTesting.scala:239)
        at dotty.tools.vulpix.ParallelTesting$$anon$4.checkTestSource$$anonfun$1(ParallelTesting.scala:285)
        at dotty.tools.vulpix.ParallelTesting$$anon$4.checkTestSource$$anonfun$adapted$1(ParallelTesting.scala:288)
        at scala.Function0.apply$mcV$sp(Function0.scala:42)
        at dotty.tools.vulpix.ParallelTesting$Test.tryCompile(ParallelTesting.scala:462)
        at dotty.tools.vulpix.ParallelTesting$$anon$4.checkTestSource(ParallelTesting.scala:288)
        at dotty.tools.vulpix.ParallelTesting$Test$LoggedRunnable.run(ParallelTesting.scala:358)
        at dotty.tools.vulpix.ParallelTesting$Test$LoggedRunnable.run$(ParallelTesting.scala:340)
        at dotty.tools.vulpix.ParallelTesting$$anon$4.run(ParallelTesting.scala:283)
        at java.base/java.util.concurrent.ForkJoinTask$AdaptedRunnableAction.exec(ForkJoinTask.java:1403)
        at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:387)
        at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1312)
        at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1843)
        at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1808)
        at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:188)
Interrupted (probably running after shutdown)
java.util.concurrent.ExecutionException: java.lang.InterruptedException

and

[info] Test dotty.tools.dotc.CompilationTests.explicitNullsRun started
[===============================>        ] completed (8/10, 0 failed, 0s)java.nio.channels.ClosedByInterruptException
        at java.base/java.nio.channels.spi.AbstractInterruptibleChannel.end(AbstractInterruptibleChannel.java:199)
        at java.base/sun.nio.ch.FileChannelImpl.endBlocking(FileChannelImpl.java:171)
        at java.base/sun.nio.ch.FileChannelImpl.size(FileChannelImpl.java:430)
        at java.base/java.nio.file.Files.createFileChannelLinesStream(Files.java:4123)
        at java.base/java.nio.file.Files.lines(Files.java:4109)
        at dotty.tools.utils$package$.toolArgsFor$$anonfun$1(utils.scala:68)
        at scala.collection.LinearSeqOps.foldLeft(LinearSeq.scala:183)
        at scala.collection.LinearSeqOps.foldLeft$(LinearSeq.scala:179)
        at scala.collection.immutable.List.foldLeft(List.scala:79)
        at dotty.tools.utils$package$.toolArgsFor(utils.scala:74)
        at dotty.tools.vulpix.ParallelTesting$TestSource.allToolArgs(ParallelTesting.scala:103)

[yilinwei]

According to the javadoc for the ExecutorService, this shouldn't happen.

The doc for shutdown states that:

Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.

Since we call awaitTermination straight afterwards with a long timeout, all the tasks ought to be finished.