tests: increase number of threads for testinfra
tests: increase number of threads for testinfra

from 4 to 8 to make testing faster.

Signed-off-by: Guillaume Abrioux <30a9df5a0293a6108675377fa1673f7aa713f915@redhat.com>

ceph/ceph-ansible,jtaleric/ceph-ansible,fgal/ceph-ansible,ceph/ceph-ansible,font/ceph-ansible,travmi/ceph-ansible,font/ceph-ansible,travmi/ceph-ansible,fgal/ceph-ansible,jtaleric/ceph-ansible