Returns list of courses that we offer to the caller for remote enrolment of their users
Since Moodle 2.0, courses are made available for MNet peers by creating an instance
of enrol_mnet plugin for the course. Hidden courses are not returned. If there are two
instances - one specific for the host and one for 'All hosts', the setting of the specific
one is used. The id of the peer is kept in customint1, no other custom fields are used.