Strongbox: Use awaitility for asynchronous tests

[fuss86]

We should get rid of org.carlspring.strongbox.cron.jobs.BaseCronJobWithMavenIndexingTestCase#expectEvent(long, long) and org.carlspring.strongbox.cron.jobs.BaseCronJobWithMavenIndexingTestCase#expectEvent() methods and simplify all subtypes of org.carlspring.strongbox.cron.jobs.BaseCronJobWithMavenIndexingTestCase by using https://github.com/awaitility/awaitility tool.

[v3rtumnus]

I could do that if no one else is working on it :)

[fuss86]

Don't hesitate to start doing it 👍

[carlspring]

@v3rtumnus ,

This would be much appreciated! Please, feel free to take this task! Also, I would like to recommend that you join our chat channel where the other developers hang out and where you could get answers and help. :)

[fuss86]

Good job, @v3rtumnus ! @carlspring it's good to be merged !