NIFI-6509 - Date related issue in unit test VolatileComponentStatusRe…

[tpalfy]

…positoryTest

VolatileComponentStatusRepositoryTest: In 'createBuffers' adding Date objects to repositories starting from 1970.01.01 00:00:00 local time (instead of GMT) - the same way as the 'start' filter parameters are created in the tests.
Minor refactor (some code duplication elimination in creating the repositories and the testing logic in a couple of unit tests.)

VolatileComponentStatusRepository: filterDates method also used 'new Date(0)' when the start parameter was null. Replaced with 'new Date(Integer.MIN_VALUE)'.
Replaced comment with a fitting annotation (@VisibleForTesting).

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[ijokarumawak]

Hi @tpalfy, thanks for sending the PR! Another JIRA NIFI-6508 and its patch were submitted before this PR, so I merged NIFI-6508 to address the timezone issue at the test. Please take a look at this commit 00f0f84

I noticed your PR addresses the issue as well as does some refactoring to improve code readability. I like more self-descriptive variable naming like you did in the PR. Now the PR has conflict, if you can address conflict, I'm happy to keep reviewing so that your change can also be merged. Thanks!

[tpalfy]

Hi @ijokarumawak,
Thanks for the update. I checked NIFI-6508 and kept that solution (mine is more complex and only better in non-existing cases - when we would create timestamps close to epoch at GMT+n).
So only the test class refactor remains in this PR.

[ijokarumawak]

Thanks for the updates @tpalfy ! The change LGTM, +1. Merging to master!