hotpot use of get_users_by_capability will cause performance issues.

get_users_by_capability is a heavy query, and should really only be used once per page load if possible. It looks like the hotpot report.php file could potentially call it 4 times on one page load. - This would likely cause a timeout issue if the hotpot module was added to a site homepage for a site that has a large number of users.

in fact - this call in function hotpot_print_report()

$teachers = get_users_by_capability($modulecontext, 'mod/hotpot:viewreport', 'u.id,u.firstname,u.lastname', 'u.lastname');

doesn't seem to be needed. and should be removed.