initial_tasks: make it possible to disable ansible
initial_tasks: make it possible to disable ansible

Introduce ceph_cm_ansible option in order to ommit 'ansible.cephlab'
task, so alternative way of target node provisioning can be selected

Signed-off-by: Kyr Shatskyy <82d0c7561ff7e9a20a19db22e8fb5b2adaa3d71e@gmail.com>

dmick/teuthology,ceph/teuthology,ktdreyer/teuthology,ktdreyer/teuthology,dmick/teuthology,SUSE/teuthology,dmick/teuthology,SUSE/teuthology,ceph/teuthology,SUSE/teuthology