Add domain name support

Add support for domain name

    docker run -i -t -h test ubuntu bash
    $>hostname
    test
    $>hostname -d
    $>hostname -f
    test
    $>cat /etc/hostname
    test

---

    docker run -i -t -h test.toto.us base bash
    $>hostname
    test
    $>hostname -d
    toto.us
    $>hostname -f
    test.toto.fr
    $>cat /etc/hostname
    test

Both changes in `/etc/hosts` and `/etc/hostname` are shown in `docker diff`