* Fix: `nextToken` value in `logs:FilterLogEvents` response
Plagiarizing freely from @bpandola and his PR #3398, I have
modified the pagination for FilterLogEvents to more closely follow
the real AWS behaviour.
Fixes#3882
* Black reformatted my code.
* Remove timezone for python2.7 compatibility.
* Hopefully fix python2.7 compatibility for real.
* Additional test for a non-matching log group name in the nextToken.