Adds checks on behat tests that require specific language installed

[alexkeel]

Resolves issue #266

Adds checks to behat tests so they're skipped rather than fail when a particular language isn't installed on the server.

[mkassaei]

Hi @trampgeek, Is there any chance to look at the PR #267

[trampgeek]

OK, I've merged that. Thanks @alexkeel and @mkassaei. Sorry about the delay - but I admit to feeling a bit skeptical about the need. All the languages in the CodeRunner test suite are part of a base install of Jobe. I don't really like the idea that someone will remove languages from Jobe - why cripple it? In particular, I regard python3 as absolutely essential as I use it in lots of custom question types. And if languages are missing on Jobe, the associated question types will all fail if a teacher attempts to use them. Are you also deleting the associated prototypes from Moodle if you're deleting the languages from Jobe?

However, the changes seem to be harmless and I assume you have some use case that has motivated this pull request.