Adjust disk monitoring limits

[OpenStack Infra]

https://review.openstack.org/240951
commit 19b63d48c779a4f48aa0b6d29464f4821669a9ac
Author: Alex Schultz <email address hidden>
Date: Mon Nov 2 11:36:08 2015 -0600

    Adjust disk monitoring limits

    This change increases the threshold limit for the corosync disk monitor
    from 100M to 512M and decreases the disk monitoring interval from 30s to
    15s. These changes are to try and provide additional time for pacemaker
    to realize a full disk and trigger a failover prior to the disks
    actually being filled.

    With this change we are also reducing the disk_free_limit configuration
    for rabbitmq from the default of 50M to 5M. When rabbitmq hits the
    disk_free_limit, it will trigger flow control which will block the
    clients. The reduction of the limit from 50M to 5M is to try and still
    have the disk limit in place for an emergency situation but provide
    additional time for corosync to try and shutdown rabbitmq before it
    blocks clients.

    DocImpact: Minimum space free set to 512M for a controller. If any
    parition on the controller (besides /boot) drops below 512M, the
    controller will migrate services off of the affected node. If space
    drops below 5M prior to services being migrated, rabbitmq consumers may
    be blocked and might have to be restarted before services function
    correctly.
    Closes-Bug: #1493520

    Change-Id: I537543ce04c4f229939fd7836daf1d62c920974b