Please review: Issue 49581 - Fix dynamic plugins test suite

[Simon Pichugin]

Hi team,
please review a PR for dynamic plugins test suite fix.

https://pagure.io/389-ds-base/issue/49581
https://pagure.io/389-ds-base/pull-request/49626
I devided it in two parts for easy review.

https://pagure.io/fork/spichugi/389-ds-base/c/9c7a76e27adfff02c40abdd4d49...
First part adds a new Plugin functionality and fixes test suite.

https://pagure.io/fork/spichugi/389-ds-base/c/6da4cd78e117e0f3f75165561ca...
And the second one moves the plugins_test.py to plugins/acceptance_test.py
and adopts it for working with fixtures.

Later it will be rebased in one commit.

Thanks,
Simon