Neutron L3 HA should be prohibited if only one controller is available

[Sergey Kolekonov]

Neutron L3 HA feature UI part was added in this patch https://review.openstack.org/#/c/242543/
It requires at least 2 controllers to work properly, but currently there's no ability to set such restriction using openstack.yaml file.
I tried to add at least a warning using the following fixture:
           restrictions:
             - condition: "settings:neutron_advanced_configuration.neutron_dvr.value == false"
               action: "none"
               message: "Neutron L3 HA requires at least 2 controller nodes to function properly"

but it doesn't work ("Save" button is unavailable)

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/255401

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/255401
Committed: https://git.openstack.org/cgit/openstack/fuel-web/commit/?id=da01069cb711c59bbacaba0777461932e7fe0508
Submitter: Jenkins
Branch: master

commit da01069cb711c59bbacaba0777461932e7fe0508
Author: Vitaly Kramskikh <email address hidden>
Date: Wed Dec 9 20:46:19 2015 +0300

    Require 2 controllers when Neutron L3 HA is enabled

    Change-Id: Ic8d1297dc31fa67bf92ee871d7e417b961929637
    Closes-Bug: #1517800

[Anastasia Palkina (apalkina)]

Verified on ISO #284

VERSION:
  feature_groups:
    - mirantis
  production: "docker"
  release: "8.0"
  api: "1.0"
  build_number: "284"
  build_id: "284"
  fuel-nailgun_sha: "eb187d0eed96226ca0d8c4513ffcafc4d09dee62"
  python-fuelclient_sha: "f96659066e522e28b389de3cc685f6f2aacca3da"
  fuel-agent_sha: "2f18b7596bc7da79d2f28c34f42620b2090d8a35"
  fuel-nailgun-agent_sha: "a33a58d378c117c0f509b0e7badc6f0910364154"
  astute_sha: "e8c753d6ce1405df78d032e88c0d5a1c6f3d17ce"
  fuel-library_sha: "15d966e164a8b8f7d94c70863bd1cc4990703ec8"
  fuel-ostf_sha: "632730169e8c01afe7fd5d78a898f00d4646358b"
  fuel-mirror_sha: "31b9df814960ec69b644ca9b689dacec0c7e10a1"
  fuelmenu_sha: "680b720291ff577f4c058cee25f85e563c96312e"
  shotgun_sha: "a0bd06508067935f2ae9be2523ed0d1717b995ce"
  network-checker_sha: "a3534f8885246afb15609c54f91d3b23d599a5b1"
  fuel-upgrade_sha: "1e894e26d4e1423a9b0d66abd6a79505f4175ff6"
  fuelmain_sha: "1577a306c2c9e7bd12f28c0e16cf3652997da004"