ceph playbook should allow incremental addition of mons and osds

[mapuri]

moved from contiv/build#22 as ansible repo is the right place for this.

+++++++++
right now the way ceph configuration is generated (as shown in the snippet from ansible/roles/ceph-common/templates/ceph.conf.j2 below) results in a dependency that all mons and osds hosts need to be configured together in single playbook run.

In a real cluster, we would need to allow incremental provisioning of new mons and osds. This issue tracks this requirement.

79 {% for host in groups[mon_group_name] %}
80 {% if hostvars[host]['ansible_hostname'] is defined %}
81 [mon.{{ hostvars[host]['ansible_hostname'] }}]
82 host = {{ hostvars[host]['ansible_hostname'] }}
83 mon addr = {{ hostvars[host]['ansible_' + monitor_interface]['ipv4']['address'] }}
84 {% endif %}
85 {% endfor %}