test: update test-run (fix slowdown on python 3)

List of changes in test-run:

* readme: add memcached to users ([PR #285][1])
* test: add integration tests ([PR #273][2])
* test: enable in continuous integration ([PR #273][2])
* Fix slowdown on Python 3 ([PR #290][3])

Updated .luacheckrc to exclude newly added 'core = tarantool' tests
(ones that check test-run itself).

[1]: https://github.com/tarantool/test-run/pull/285
[2]: https://github.com/tarantool/test-run/pull/273
[3]: https://github.com/tarantool/test-run/pull/290