fix(builder): ssh timeout to prevent intermediary firewalls/loadbalancers from dropping connection    

 
    Currently the Deis-builder loses connection to cilents sometimes when tbere
    are intermediaries that monitors the connection and drops it after a certain
    interval (eg AWS Load Balancers have a 5 min timeout) while the Builder is
    busy with some activities such as tarring a file etc.
    
    This will ensure a ssh-keepalive is sent every minute to keep the connection
    open.
    
    TODO: Tests needs to be created with mock Firewalls in the middle that are
    configured to drop connection as specific intervals, and we need to demonstrate
    that the builder does not lose connection past those period when connected
    to by a client.
    
    Fixes #1046, #1195