Console messages should be suppressed in Write-Log for non-interactive consoles

[lisaong]

Write-Log currently outputs both to the console and the text log file.  

For some server applications, store broker can be invoked through a non-interactive console, which causes Write-Log to fail if console logging is enabled for a given log level (typically the default or "Info" level and above). 

If the console is non-interactive, there is no point logging to it anyway, so console output should be suppressed.