docs: Fix link to ceph/qa suites in intro_testers.rst
docs: Fix link to ceph/qa suites in intro_testers.rst

According to [1], ceph-qa-suite is deprecated (last commit is from
2016) and the QA suites are now in the ceph git repo in the qa/
directory. So point to that directory.

[1] https://github.com/ceph/ceph-qa-suite/

dmick/teuthology,SUSE/teuthology,ktdreyer/teuthology,SUSE/teuthology,ktdreyer/teuthology,ceph/teuthology,SUSE/teuthology,dmick/teuthology,dmick/teuthology,ceph/teuthology