Bump to current (3.6.x) behat version

Right now we are running behat 3.5.x, this issue is about:

1) Bump it to current 3.6.x series.
2) Consider associated / dependent components that also can be updated.
3) Verify that everything continues passing ok, for all php versions supported on every branch.

Note that, in order to be able to test this with php74, we need all the current (5-6) issues in the php74 epic to be applied. In the mean time, I'll be running php74 tests against some branches containing all them, just to confirm that everything is ok. This doesn't stop this issue to progress, just we must ensure that php74 works ok.

(this is part of the release process, review phpunit and behat versions 8 weeks before releases)