fleetctl appends port number in ~/.fleetctl/known_hosts

By default when generating a known_hosts file, fleet appends the port number.  This is problematic for two reasons.  
 1. if the port number is 22 it should not be included
 1. if the port number is _not_ 22 then the ip address should be enclosed in square braces and the port should be appended afterwards (e.g. [192.168.1.1]:22).  This is because IPv6 addresses utilize colons as a delimiter.  For more information, man sshd - section "SSH_KNOWN_HOSTS FILE FORMAT".