MDL-38619 behat: New test

According to MDLQA-1177, an administrator
can create a cohort and add users to it.
MDL-38619 testing: Adapter to cohorts data generator
MDL-38619 behat: Step definition to add enrolment methods to courses
MDL-38619 behat: New test

According to MDLQA-1445, an administrator
can upload users to a cohort.