make fastestmirror plugin present

[Jeffrey Zhang]

i found something[0] which explain how the fastestmirror works.

> Yum has a plugin, fastestmirror. The purpose of that plugin is to determine the fastest available mirror and makes yum download from it, not some random one. Usually, this plugin works very well, but this time it didn't. I tried to reset everything with
> fastestmirror plugin determines which mirror is the best one based on measuring how much time is necessary to establish connection with a mirror, and then it immediately disconnects.

So,

1. fatestmirror don't cache anything in the disk.
2. it will save much time to get the fastest mirror, rather than random use one by one.

So, it will be OK and helpful to make this plugin present.

[0] http://sgros.blogspot.com/2012/10/yum-and-fastestmirror-plugin.html

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/255938
Committed: https://git.openstack.org/cgit/openstack/kolla/commit/?id=aabafd343b7ce2e94a2adf9400525342284bb937
Submitter: Jenkins
Branch: master

commit aabafd343b7ce2e94a2adf9400525342284bb937
Author: Jeffrey Zhang <email address hidden>
Date: Thu Dec 10 23:25:40 2015 +0800

    Do not purge yum-plugin-fastestmirror package

    It will be helpful for speed up the package installation.

    Closes-Bug: #1525514
    Change-Id: Id40a0afa30dd0a142bee3b13f7622cb0d42d9298

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/liberty
Review: https://review.openstack.org/268838

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/268838
Committed: https://git.openstack.org/cgit/openstack/kolla/commit/?id=0ece2b7773c84a0e22eaadf0e2e511a40dec9810
Submitter: Jenkins
Branch: stable/liberty

commit 0ece2b7773c84a0e22eaadf0e2e511a40dec9810
Author: Jeffrey Zhang <email address hidden>
Date: Thu Dec 10 23:25:40 2015 +0800

    Do not purge yum-plugin-fastestmirror package

    It will be helpful for speed up the package installation.

    Closes-Bug: #1525514
    Change-Id: Id40a0afa30dd0a142bee3b13f7622cb0d42d9298
    (cherry picked from commit aabafd343b7ce2e94a2adf9400525342284bb937)