update flavor admin docs
update flavor admin docs

- This change updates the admin flavor docs
  to reflect the use of osc to update flavor
  descriptions

- This change documents that modifcations to
  flavor extra_specs are not reflected in an
  instance's embedded flavor.

Change-Id: I0f206d9db70465d8ce6b1404f546f3e00eeb6e23

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