Add troubleshooting information for when a Compute instance log is empty

[Don Domingo]

This occurs when the Compute service is trying to retrieve the log output of the guest via a serial console but the guest itself is not sending output to the console.

It would be useful to add instructions on how to quickly resolve this problem.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/76430

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/76430
Committed: https://git.openstack.org/cgit/openstack/openstack-manuals/commit/?id=53b7635a195685544444863ef9ad5a82fae4ffec
Submitter: Jenkins
Branch: master

commit 53b7635a195685544444863ef9ad5a82fae4ffec
Author: Don Domingo <email address hidden>
Date: Wed Feb 26 14:25:06 2014 +1000

    Add solution for when instance log output is empty

    A Linux instance has to be configured to send log output to the serial
    console whenever the Compute service collects log output from there.
    Otherwise, the log output will be empty. Added this as a
    troubleshooting tip to Cloud Admin Guide.

    Change-Id: I5adb28c2d73c41792c1d67f51e11edfc7474ed99
    Closes-Bug: #1284962

[OpenStack Infra (hudson-openstack)]

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