Do not include colon if host_port has a value of ''

[fixes #79313728]

A little extra insurance in case a human chooses to pass an empty value of port['host_port']. Docker will only dynamically assign a port when the run string is formed as '-p 3000' and not '-p :3000'

Also updating the UI to not pass host_port if the user leaves it empty.
Can we get an itsy, bitsy test for this?