Since Moodle 2.6.4 Teacher role cannot add "cohort sync" enrolment method to a course, problem still persists in Moodle 2.7.1.
The help file states that https://docs.moodle.org/26/en/Capabilities/enrol/cohort:config
The required capabilities for setting up a cohort sync are:
moodle/course:enrolconfig in the course context
moodle/cohort:config in the course context
moodle/cohort:view in the same context as cohort
But there is no moodle/cohort:config option when defining roles.