remove ceph-release and call yum clean all

This helps when going through different ceph versions and wanting to upgrade.

    $ ceph-deploy purge node2
    [ceph_deploy.cli][INFO  ] Invoked (1.3.5): /Users/alfredo/.virtualenvs/ceph-deploy/bin/ceph-deploy purge node2
    [ceph_deploy.install][DEBUG ] Purging from cluster ceph hosts node2
    [ceph_deploy.install][DEBUG ] Detecting platform for host node2 ...
    [node2][DEBUG ] connected to host: node2
    [node2][DEBUG ] detect platform information from remote host
    [node2][DEBUG ] detect machine type
    [ceph_deploy.install][INFO  ] Distro info: CentOS 6.4 Final
    [node2][INFO  ] purging host ... node2
    [node2][INFO  ] Running command: sudo yum -y -q remove ceph ceph-release
    [node2][INFO  ] Running command: sudo yum clean all
    [node2][DEBUG ] Loaded plugins: fastestmirror
    [node2][DEBUG ] Cleaning repos: base epel extras updates
    [node2][DEBUG ] Cleaning up Everything
    [node2][DEBUG ] Cleaning up list of fastest mirrors