enable passing of cucumber runtime args

[calebkeene]

with newer cucumber versions (>5) and rails >= 6.1 on semaphore there is no output when running cucumber tests unless --verbose is explicitly passed and this can make debugging quite difficult. It's currently not possible to pass in these cucumber args to the cucumber_booster script. Allow it to load args from an environment variable that can be set in the build container

e.g.

CUCUMBER_ARGS="--backtrace --verbose --format pretty" cucumber_booster --job $SEMAPHORE_JOB_INDEX/$SEMAPHORE_JOB_COUNT

will provide a nice verbose output that allows debugging of any test failures without having to SSH in to a build container and poke around in the logs

[calebkeene]

@shiroyasha @bmarkons can we merge?