Gns 80 cloud image

For review.
Replace with something like:
```
    rc_local = ""
    if on_boot:
        rc_local = "echo '/usr/local/bin/gns3-server' >> /etc/rc.local\n\n" 
    script = textwrap.dedent("""
    <stuff goes here>
    git clone --branch #{git_branch} #{git_url}
    <more stuff>
    #{rc_local}
    touch /tmp/gns-install-complete
    """)
```

This makes it more script-like without going all the way to Jinja templates..