Bug 1772792: Update behat for php7.2

- changed composer dependencies to make 7.2 work
- switched to carat syntax which allows upgrade up to anything below the next major version.
- fixed use of count to check for null in Behat2Renderer.php
- tested dependencies with php 5.6, 7.0, 7.1, 7.2. You do need to
  manually delete the composer.lock file and run make initcomposer to resolve issues.

behatnotneeded

Change-Id: I725d8ac6a2f8ca9d67c95d7d6184882a364c0762