Enable multipath usage on all OpenStack hosts

[OpenStack Infra]

https://review.openstack.org/257425
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commit 8b0bae21cd660d65bd87509849c4cedfeb9fd7be
Author: Bjoern Teipel <email address hidden>
Date: Mon Dec 14 09:01:06 2015 -0600

    Enable multipath usage on all OpenStack hosts

    This fix adds the multipath-tools package to all nova
    nodes in order to support iscsi-multipath inside nova.
    Additionally when using multipath, the stock AIO limit
    per process (fs.aio-max-nr) is too low and needs to be
    increased to at least 128k.

    In order to enable this feature in nova the following override
    needs to be configured:

    nova_nova_conf_overrides:
      libvirt:
          iscsi_use_multipath: true

    This is a backport combining two patches:
     - https://review.openstack.org/256082
     - https://review.openstack.org/257104

    DocImpact
    Closes-Bug: #1524957
    Change-Id: I36da282043ce864c8a1fb69a1ee02e3a273c14e4