waitForJobs: don't wait for setInterval() jobs.

[alexgo91]

In JavaScriptJobManagerImpl, method waitForJobs() waits for all kinds of
jobs, including never-ending jobs created by setInterval(). The caller
wouldn't expect this method to block indefinitely and it causes some
scenarios to get stuck.
Also, for correctness - synchronized block should wrap final job count
check as well.

[rbri]

What about using waitForJobsStartingBefore(final long delayMillis, final JavaScriptJobFilter filter)?

[alexgo91]

I am thinking about the user of HtmlUnit - it will be more simpler for him to say "wait for all tasks", instead of defining filter + delay (which is not always clear as it depends on the performance of the website).
The wait command is mostly used as part of a larger test scenario, and therefore the user just wants the website to finish loading and become ready, including all tasks. It's easier to call waitForJobs - and there shouldn't be a scenario in which a user expects this call to block forever (like happens in case of setInterval() jobs)