[docs] Improve documentation about OpenStack Storage nodes and rolls

[Meg McRoberts]

Need to improve information about Storaghe
- Improve architecural info in http://docs.mirantis.com/openstack/fuel/fuel-5.0/reference-architecture.html#storage-architecture
- Add a chapter to the Planning Guide about "Designing Storage for your Environment"
- Improve Terminology articles about Swift, Cinder, Ceph, etc
- Add information to the Operations Guide about administering and troubleshooting your Storage roles/nodes
- Add information to the Operations Guide about measuring and improving the performance of your Storage roles/nodes
- Be sure that adequate supporting information is available for filling in the Storage-related configuration screens:
  - http://docs.mirantis.com/openstack/fuel/fuel-5.0/user-guide.html#storage-background-for-cinder-and-glance
  - http://docs.mirantis.com/openstack/fuel/fuel-5.0/user-guide.html#assign-a-role-or-roles-to-each-node-server
  - http://docs.mirantis.com/openstack/fuel/fuel-5.0/user-guide.html#storage

The information needs to be complete, although it can link to Community docs for details as appropriate

[Fabrizio Soppelsa (fsoppelsa)]

An important point often emerging from interaction with users on IRC is mostly about Ceph.

Users sometimes ask to improve the operating guide with some Ceph basic troubleshooting on MOS.

I suggest also to significantly expand the part explaining Ceph in the planning guide and add some advices, like that with Ceph storage, raw images is reccomended, and why that.

An option in the settings that is not covered at all is "Use qcow2 format for images". It's important to add some notes, because the checkbox's label is confusing users.