MDL-43738 behat: New step to adapt to radio buttons behaviour

Now we interact with radio fields through it's value
or text.
MDL-43738 behat: Backporting new 2.7 methods to 2.6

We encourage backporting new feature files, adding
here also these Moodle 2.7 new step definitions so
future features will be easier to backport as we
would be able to directly cherry-pick them.