Incorrect (for php70) return :void detected in behat stuff

Requirements

1. web server and CLI using PHP 7.0.x (behat will tell you if both are ok or there are any differences)

Preparation

1. Copy the attached 67009.feature file into the lib/tests/behat/ directory.
2. Init behat (with the flag: -a)
3. Run behat with flags: --tags '@mdl67009'
4. Verify that you get 3 failures (one for each suite/theme: default, clean, more).
5. Edit config.php and add: $CFG->behat_pause_on_fail = true;
6. Run behat again, with same flags: --tags '@mdl67009'
7. Verify that you get the execution paused 3 times (press <<enter>> after every one) with message:

   Scenario failed. Paused for inspection. Press Enter/Return to continue.

   Exception follows:

   Link matching locator "Participants" not found.

8. Verify that after the 3rd <<enter>> the execution ends and the 3 failures are reported exactly like they where in points 3 & 4, more exactly:
   1. a list, 001, 002, 003 of failures and then, at the end
   2. the standard execution summary with failed scenarios, steps, time...