commit cf44f0ab7d add server
concepts for the servers, some TODOs for other actions,
this patchs add the items.
Some comments are copied from support matrix doc
http://docs.openstack.org/developer/nova/support-matrix.html
which mainly talked about virt layer support while this doc more
talk about server concepts.
Partially implements blueprint complete-todo-in-api-concept-doc
Change-Id: I08c97c78b334bd17b37492ac60a7489ac6fe07de