Flush appenders before stopping

[zUniQueX]

Attempt to fix an unstable test in the class TlsSocketAppenderFactoryTest.

Problem:

loggingFactory.reset() must be called in order to receive the logged messages because it closes the OutputStream of the Socket in the appender. The relevant call is detachAndStopAllAppenders() which eventually closes the appender but maybe discards messages to be written asynchronously.

If the appender is closed before all asynchronously messages are written, the test fails. This leads to a race condition between writing the log messages and closing the appender.

Solution:

loggingFactory.stop() will attempt to flush outstanding log messages, so the messages should all be written when the appender eventually gets stopped.

[gitpod-io]