Add CellsV2 FAQ about API design decisions
Add CellsV2 FAQ about API design decisions

At the Stein summit (and previous discussions) the topic of exposing
cellsv2 out of the API came up again. This patch adds two FAQ entries
reflecting my notes from early design decisions about why we did not
want to do that, along with more recent examples, such as FFU.

These are my feelings on the subject and I was asked to put these into
FAQ form for posterity to make the discussion easier in the future. I
would recommend that we agree on these and then codify them here.

Change-Id: I0499e141456fcca63f95bad25503c4e86c6aa369

openstack/nova,klmitch/nova,klmitch/nova,mahak/nova,rahulunair/nova,mahak/nova,mikalstill/nova,mikalstill/nova,rahulunair/nova,rahulunair/nova,klmitch/nova,mikalstill/nova,klmitch/nova,openstack/nova,mahak/nova,openstack/nova