logviewer: check if port is available

[erikdw]

In our new (as of PR #212) functionality to auto-launch logviewers, we should try to ensure the port is actually available. Otherwise the storm logviewer will appear to come up even though the port wasn't bindable.

[erikdw]

One idea: maybe a wrapper / initial cmd to be executed which needs to succeed before we launch the logviewer. Where that cmd could be something like:

% sudo netstat -anpl | grep -e ':8080\s\s*.*LISTEN'
tcp        0      0 :::8080                     :::*                        LISTEN