purge-cluster: Add support for user prompt
purge-cluster: Add support for user prompt

Add support for user prompt before purging the cluster. This
ensure that accidental invocation of purge-cluster won't
purge the cluster. Defaults to no purging, unless user either
says 'yes' on the prompt or invokes the playbook with:
`-e ireallymeanit=yes`. This also aligns neatly with ceph cli's
--yes-i-really-mean-it option

Signed-off-by: Deepak C Shetty <a32a1308dee89bfc80d85f301426ba0a20e60d60@redhat.com>

guits/ceph-ansible,ceph/ceph-ansible,WingkaiHo/ceph-ansible,guits/ceph-ansible,jfcoz/ceph-ansible,travmi/ceph-ansible,albertomurillo/ceph-ansible,jsaintrocc/ceph-ansible,jtaleric/ceph-ansible,jtaleric/ceph-ansible,WingkaiHo/ceph-ansible,verdurin/ceph-ansible-1,font/ceph-ansible,dang/ceph-ansible,WingkaiHo/ceph-ansible,fgal/ceph-ansible,mcsage/ceph-ansible,travmi/ceph-ansible,fgal/ceph-ansible,jsaintrocc/ceph-ansible,ceph/ceph-ansible,rootfs/ceph-ansible,albertomurillo/ceph-ansible,font/ceph-ansible,albertomurillo/ceph-ansible,jfcoz/ceph-ansible,mcsage/ceph-ansible,dang/ceph-ansible,verdurin/ceph-ansible-1,rootfs/ceph-ansible,bengland2/ceph-ansible,bengland2/ceph-ansible