traffic_ctl - Use better format output options.

[brbzull0]

Use better output format options to display traffic_ctl JSONRPC messages.
all,req,resp are now grouped into rpc.

$ traffic_ctl config get variable --format rpc
 --> {request}
 <-- {response}
 variable 123

[bryancall]

We had a discussion in the weekly PR/issue review meeting and most people thought --output would mean sending it to a file. Leaving it as --format or --output-format might be better.

[brbzull0]

We had a discussion in the weekly PR/issue review meeting and most people thought --output would mean sending it to a file. Leaving it as --format or --output-format might be better.

fair enough, will leave it as --format then!
Thanks!

[jrushford]

looks good and tests ok.