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 45 seconds 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 (#1275) 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 = 45`
       `exit`
2. Restart the service:
       `sudo systemctl restart systemd-sysctl.service`
    
TODO: Add tests to check the tcp timeout is working.