tests: allow defining arbitrary number of OSDs
tests: allow defining arbitrary number of OSDs

Some tests might want to set this since number of devices will not
necessarily map to number of OSDs

Signed-off-by: Alfredo Deza <3f4d00ffa77e6441ab2d23c25a618925d2383b02@redhat.com>

fgal/ceph-ansible,ceph/ceph-ansible,ceph/ceph-ansible,fgal/ceph-ansible