apps: fix shared request state

proper fix for #424
Ulterior Motivation: this timing library really isn't about "msgs" (I already use it elsewhere) I was trying to move this specific naming of `requests` or `messages` out of this file so it can be re-used for other things. The balance i was landing on was to pass in a prefix w/o going too far down that road to have to pass in a full format string for all the entries.

sidenote: one could argue for the nsq_to_http use case the per-address timings should say 'requests' not 'messages' and only the global per-message timing should be 'messages'.