Nova change I565617e05acf33e6254ea091b88d975270ffde05 added
the support for creating a server with tagged VIFs and BDMs
with the xenapi driver, but did not contain a release note.
This adds the release note, and much of the text is copied
from Tempest change I9fe520bc9b68d0bc7f879617f2cd27dd1029e4de.
Part of blueprint virt-device-role-tagging-xenapi
Change-Id: I330087944203ab6aa9cf64fd4d3f1909ce44b435