fix python3 compatibility in jinja2 template.
fix python3 compatibility in jinja2 template.

rename iterkeys to keys

jsaintrocc/ceph-ansible,jtaleric/ceph-ansible,jsaintrocc/ceph-ansible,albertomurillo/ceph-ansible,guits/ceph-ansible,WingkaiHo/ceph-ansible,fgal/ceph-ansible,guits/ceph-ansible,ceph/ceph-ansible,albertomurillo/ceph-ansible,bengland2/ceph-ansible,fgal/ceph-ansible,font/ceph-ansible,ceph/ceph-ansible,travmi/ceph-ansible,albertomurillo/ceph-ansible,jtaleric/ceph-ansible,WingkaiHo/ceph-ansible,bengland2/ceph-ansible,travmi/ceph-ansible,font/ceph-ansible,WingkaiHo/ceph-ansible