Runtime and log output for `SSLCertificateTest` needs to be improved

[chrjohn]

SSLCertificateTest is a crucial test to ensure that SSL/TLS is working as intended.
However, its runtime is nearly half of the complete runtime of the CI job (more than 20 minutes vs 45 minutes of the complete job) and it is logging more than a third of the amount of log lines of the CI job (nearly 45k lines vs. 120k lines).

Ideas:

1. There is a timeout of 15 seconds when waiting if an exception occurs. We should lower that timeout to say 7 seconds and at the same time set the HeartBtInt to 5 seconds. So when we have exchanged heartbeats we could be pretty sure that the session is up and working. Nonetheless we should test that no exceptions occur.
2. We should not log exceptions multiple times if they are expected. E.g. for methods that are named like "shouldFailWhen..." we should not log the exceptions with complete stack trace but only log the exception message. This could be changed in the exceptionCaught callback of the connector.
3. For the tests that are asserting if an exception was not thrown: the tests are testing sequentially for every connector if an exception was not thrown via a latch (see point 1 in this list). This means that we are waiting multiple times in a row that no exception was thrown. We should do this in parallel and fail if any of the latches reported an exception.