Improve support for more convention patterns

This MR solves an issue when multiple convention patterns for membership tests are used.

Before we had the problem that a pattern like VO_MEMBER_CONVENTIONS: 'gfz:*,*:gfz-sms-member,*:ufz-sms-member,*:kit-sms-member,*:fzj-sms-member' would only work for the gfz:* (as there is no rule convention part) and the *:gfz-sms-member (as this is then the next) but not for the *:ufz-sms-member (as the function for the check already returned False).

With this change we test for all of the convention checks.