fix(coreOS): tcp timeout to prevent intermediary firewalls/loadbalancers...

    The default tcp-keepalive on CoreOS is 7200seconds (2 hours), which is standard across linux.
    This will change that to 4 mins so that we send a tcp-keepalive packet through the connection
    to prevent the intermediary from dropping the connection.
    
    We saw occurances of this in the deis-builder when it makes a post request to controller during
    'launching...'.
    
    NOTE: The cluster needs to be redeployed for this to work.
    
    For Existing Clusters: Please follow these steps:
    1. Login to each of the instances and run the following
       sudo su -
       create a new file called /etc/sysctl.d/shorter-tcpkeepalive.conf with this content: net.ipv4.tcp_keepalive_time = 240
       exit
    2. Restart the service:
       sudo systemctl restart systemd-sysctl.service
    
    TODO: Add tests to check the tcp timeout is working.