This patch is part of the solution for LP #2037294 and updates the
documentation to explain the new "enable-chassis-as-extport-host"
configuration as well as enhancing the documentation in general
to better explain each configuration, database information and
high availability for external ports.
Change-Id: Iad048a71653dc791fc27585b509c02470e5d08a2
Related-Bug: #2037294
Signed-off-by: Lucas Alvares Gomes <lucasagomes@gmail.com>