Allow operators to override ceph config section parameters other than "global"

It's not an unusual scenario seeing operators customizing the ceph config section parameters.
Using TripleO is pretty simple do that because there is the CephConfigOverride template variable that maps all the required info to be placed into the global section [1].
The idea behind this blueprint is to give the opportunity to override parameters in different sections of ceph.conf like we've done with the global section.
According to the ceph doc [2] we have these available sections:

* global
* mon
* osd
* mgr
* mds
* client

and for instance, in the same way of CephConfigOverride, we can provide an Osd override parameter to collect all the extra info that operators want to override in the "osd" section and then pass them to the ceph-ansible playbook to build the appropriate ceph.conf file.

We can extend this concept to the other sections, allowing operators to add in TripleO all the informations they want to override on ceph.conf.

[1] https://github.com/openstack/tripleo-heat-templates/blob/master/deployment/ceph-ansible/ceph-base.yaml#L368
[2] http://docs.ceph.com/docs/nautilus/rados/configuration/ceph-conf/#configuration-sections