Add behat generators for grades grade

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Closing as fixed!

Passing on CiBoT's behalf.

Thanks, Noel. Patches pulled in for 311 and 39. Sending back to testing!

I've just opened an issue explaining the problem I found during testing: https://moodle.atlassian.net/browse/MDL-75103#icft=MDL-75103

Thanks for checking @Eloy Lafuente,

It seems like I modified that step in 39 and 311 whilst doing a cherry-pick from master, I've fixed it now and tested locally to make sure that it works. I added a new commit in both the 39 and 311 branches, instead of ammending the previous ones (because they had been merged so I shouldn't modify them). I think merging those should fix it.