Add some data generator funtions to phpunit testing suite (Bug #1307777)
- Replaces require_user and require_test_user with create_test_user
- Added create_test_group and create_test_institution

Change-Id: I8f2acbeef986943cbb4712f47226456fdf3d9570
Signed-off-by: Nathan Lewis <nathan.lewis@totaralms.com>
Signed-off-by: Yuliya Bozhko <yuliya.bozhko@totaralms.com>