Vendoring packages (using git subtree)

```./contrib/vendor -l``` will list additional packages that might be vendored
```./contrib/vendor -v <package url>``` will vendor a specific package
Eg: ```./contrib/vendor -v github.com/kraman/go-netfilter-queue```

Vendoring sets up a subtree. See [subtree docs](https://github.com/git/git/blob/master/contrib/subtree/git-subtree.txt) for more detail on merging/splitting subtrees.

Already pushed subtree branches to repo:
* [subtree_github.com_docopt_docopt.go](https://github.com/openshift/geard/tree/subtree_github.com_docopt_docopt.go)
* [subtree_github.com_fsouza_go-dockerclient](https://github.com/openshift/geard/tree/subtree_github.com_fsouza_go-dockerclient)
* [subtree_github.com_godbus_dbus](https://github.com/openshift/geard/tree/subtree_github.com_godbus_dbus)
* [subtree_github.com_kraman_go-netfilter-queue](https://github.com/openshift/geard/tree/subtree_github.com_kraman_go-netfilter-queue)
* [subtree_github.com_kraman_libcontainer](https://github.com/openshift/geard/tree/subtree_github.com_kraman_libcontainer)
* [subtree_github.com_openshift_go-json-rest](https://github.com/openshift/geard/tree/subtree_github.com_openshift_go-json-rest)
* [subtree_github.com_openshift_go-systemd](https://github.com/openshift/geard/tree/subtree_github.com_openshift_go-systemd)
* [subtree_github.com_spf13_cobra](https://github.com/openshift/geard/tree/subtree_github.com_spf13_cobra)
* [subtree_github.com_spf13_pflag](https://github.com/openshift/geard/tree/subtree_github.com_spf13_pflag)
* [subtree_github.com_syndtr_gocapability](https://github.com/openshift/geard/tree/subtree_github.com_syndtr_gocapability)
* [subtree_code.google.com_p_gopacket](https://code.google.com/p/gopacket)


Note: Since I cannot push the configuration for upstreams, you will need to recreate upstreams. Example upstream in your .git/config will looks like:

    [remote "vndr_github_com_fsouza_go-dockerclient"]
            url = http://github.com/fsouza/go-dockerclient
            fetch = +refs/heads/*:refs/remotes/vndr_github_com_fsouza_go-dockerclient/*
    [branch "subtree_github_com_fsouza_go-dockerclient"]
            remote = vndr_github_com_fsouza_go-dockerclient
            merge = refs/heads/master

Corresponding commands would be:

    git remote add vndr_github_com_fsouza_go-dockerclient http://github.com/fsouza/go-dockerclient
    git branch -u vndr_github_com_fsouza_go-dockerclient/master subtree_github_com_fsouza_go-dockerclient