Updates for jdk17+
fix imports
use randomBoolean()
testCommonPoolThreadContextClassLoader: add positive assertions for setContextClassLoader
8215359: InnocuousForkJoinWorkerThread.setContextClassLoader needlessly throws
unused imports
use await(CountDownLatch) pervasively
8176551: testCommonPoolThreadContextClassLoader fails with "Should throw SecurityException"
JDK-8172726: ForkJoin common pool retains a reference to the thread context class loader
add testCommonPoolThreadContextClassLoader
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