qa/cephfs: fix build failure for mdtest project

qa/cephfs: fix build failure for mdtest project

To fix the mdtest job failure (which happens because building mdtest
project fails) do -

1. Use ior projects intead of mdtest project bcecause latter was merged
   into former. See:
   https://github.com/MDTEST-LANL/mdtest/blob/master/README.md

2. Purge mpich package and then install it again. This is a vital step
   that's needed to build ior project on Ubuntu 22.04.

Fixes: https://tracker.ceph.com/issues/61574
Signed-off-by: Rishabh Dave <ridave@redhat.com>