Expose DisableTerminalOutput setting to CLI

[bebehei]

This is useful for shell-scripting when used in combination with another exporter (like raw CSV or Cloudwatch or Prometheus)

It just exposes the flag -s or --silent, so you can use even the CLI tool noninteractively. For shell-users, who are much better in programming bash/zsh it is easier for them instead of using cassowary as a Go library.

[rogerwelin]

changes removes the spinner and status-text but you also need to disable the metrics being printed to the console.

in the runLoadTest func please do the following:

if !c.DisableTerminalOutput {
   outPutResults(metrics)
}

[bebehei]

I've added the requested change by you, @rogerwelin.

[rogerwelin]

Thank you @bebehei for the contribution!