MerkleDbDataSourceTest.preservesInterruptStatusWhenInterruptedClosing() is unstable

[artemananiev]

The test fails intermittently:

> Task :swirlds-merkledb:timingSensitive
  com.swirlds.merkledb.MerkleDbDataSourceTest > preservesInterruptStatusWhenInterruptedClosing()

    org.opentest4j.AssertionFailedError
        at app//com.swirlds.merkledb.MerkleDbDataSourceTest.createAndApplyDataSource(MerkleDbDataSourceTest.java:786)
    Caused by: org.opentest4j.AssertionFailedError: Thread interrupt status should NOT be cleared (two total interrupts) ==> expected: <2> but was: <3>
        at app//com.swirlds.merkledb.MerkleDbDataSourceTest.lambda$preservesInterruptStatusWhenInterruptedClosing$48(MerkleDbDataSourceTest.java:558)

If it's changed from "Test" to "RepeatedTest(10)", the very first run fails, and then all subsequent runs are successful.

[artemananiev]

I don't know what this test is actually checking. Probably, it should be just removed.

When the test fails like above, the three interrupt() calls are:

• Direct call from the test itself: closingThread.interrupt()
• A call from MerkleDbDataSource.shutdownThreadsAndWait(), when it catches an InterruptedException while waiting for all executors are shut down
• A call from jdk.internal.loader.Resource.getBytes(), when it tries to load a class like MemoryUtils

Apparently, the third call is intermittent, it really depends on whether the class has or has not been loaded yet.

[artemananiev]

Even if all the classes has been loaded, the test may fail because of extra interrupt() calls in weird places, for example:

at com.swirlds.merkledb.MerkleDbDataSourceTest$InterruptRememberingThread.interrupt(MerkleDbDataSourceTest.java:901)
	at java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:723)
        ...
	at org.apache.logging.log4j.core.util.CloseShieldOutputStream.write(CloseShieldOutputStream.java:53)
        ...
	at org.apache.logging.log4j.spi.AbstractLogger.info(AbstractLogger.java:1345)
	at com.swirlds.merkledb.MerkleDbDataSource.close(MerkleDbDataSource.java:776)
	at com.swirlds.virtualmap.datasource.VirtualDataSource.close(VirtualDataSource.java:58)
	at com.swirlds.merkledb.MerkleDbDataSourceTest.lambda$preservesInterruptStatusWhenInterruptedClosing$47(MerkleDbDataSourceTest.java:551)
	at java.base/java.lang.Thread.run(Thread.java:1583)

It's nearly impossible to take all these into account. My proposal is either to delete the test case completely, or change it to check the number of interrupt() calls to be 2 or greater rather than 2 exactly.