NSX - add note in configuration files regarding distributed routers

[Salvatore Orlando]

In order to leverage distributed routing with the NSX plugin - the replication_mode parameter should be set to 'service'.
Otherwise the backend wil throw 409 errors resulting in 500 NSX errors.

This should be noted in the configuration files.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/113403

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/113403
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=0ac15ad5d7902ef30d495acf737c90ba9377566a
Submitter: Jenkins
Branch: master

commit 0ac15ad5d7902ef30d495acf737c90ba9377566a
Author: Salvatore Orlando <email address hidden>
Date: Mon Aug 11 16:29:42 2014 -0700

    NSX: fix wording for configuration option

    This patch clarifies that in order to use NSX distributed
    routers, the replication_mode parameter should be set to
    'service'. This is already its default value, so no further
    change is needed beyond clarifying wording.

    Change-Id: I446c428ecf8c0bf7f6947e69562d60a7fb4383ed
    Closes-Bug: #1355502