[bug/typo] cdh plugin yum install option "-y" missing

[JiHyun Song]

at sahara/plugins/cdh/commands.py

```
def install_packages(remote, packages, timeout=1800):
    distrib = _get_os_distrib(remote)
    if distrib == 'ubuntu':
        cmd = 'RUNLEVEL=1 apt-get install -y %s'
    elif distrib == 'centos':
        cmd = 'yum install %s'
    else:
        raise ex.HadoopProvisionError(
            _("OS on image is not supported by CDH plugin"))

    cmd = cmd % ' '.join(packages)
    _root(remote, cmd, timeout=timeout)
```

when I install cdh using sahara with CentOS image, it occurs timeout exception because of missing option "-y".

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/307722

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/307722
Committed: https://git.openstack.org/cgit/openstack/sahara/commit/?id=ac82ffcaad4ee9d959350c4975a54ffe27ed8bdd
Submitter: Jenkins
Branch: master

commit ac82ffcaad4ee9d959350c4975a54ffe27ed8bdd
Author: JiHyunSong <email address hidden>
Date: Tue Apr 19 20:37:37 2016 +0900

    cdh plugin yum install option "-y" missing

    when I install cdh using sahara with CentOS image,
    it occurs timeout exception because of missing option "-y".

    Change-Id: Iee9a5d6ab7868fc426c6a82bc7a45228680f8cc6
    Closes-Bug: #1566278

[Doug Hellmann (doug-hellmann)]

This issue was fixed in the openstack/sahara 5.0.0.0b1 development milestone.