fix(coreOS): tcp timeout to prevent intermediary firewalls/loadbalancers from dropping connection

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.