Add solution of unable restart 'nova-compute' service.

[Chason Chan]

"If the nova-compute service fails to start, check /var/log/nova/nova-compute.log. The error message AMQP server on controller:5672 is unreachable likely indicates that the firewall on the controller node is preventing access to port 5672."

This note just give the reason of unable to restart the 'nova-compute' service.
I think it will be better if we add the solution of this issue.
-----------------------------------
Release: 0.1 on 2016-10-19 07:26
SHA: d6e69bfb174072f4400919ff3472747e61ccf1e7
Source: http://git.openstack.org/cgit/openstack/openstack-manuals/tree/doc/install-guide/source/nova-compute-install.rst
URL: http://docs.openstack.org/newton/install-guide-ubuntu/nova-compute-install.html

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/431386

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/431386
Committed: https://git.openstack.org/cgit/openstack/openstack-manuals/commit/?id=7653dacb7c4b37f69c5c687a9848f1e897e3fec4
Submitter: Jenkins
Branch: master

commit 7653dacb7c4b37f69c5c687a9848f1e897e3fec4
Author: chenxing <[e-mail]>
Date: Thu Feb 9 08:26:10 2017 +0000

    [install] Add more content about the solution of the issue

    Change-Id: I6e06e427c2543e74ff50a829b96a473fb2d3e7e0
    Closes-Bug: #1634806

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/openstack-manuals 15.0.0 release.