[httperf] Improving output readability/usability

[Mark Nottingham]

Just thinking out loud, it would be good if httperf flagged problems  
in the test more obviously, so that users would know that there's a  
problem with the test.

In particular, if the CPU utilisation is too low, or if there are any  
"fd-unavail", "addrunavail", "ftab-full", "other" errors, we know  
that there's a client-side problem, and httperf should alert the  
user; probably with a big all-caps warning message, and perhaps by  
exiting with a non-zero status.

There's a lot more that could be done, of course, but that seems like  
a minimal change that would greatly help the tool's usability.

Cheers,

--
Mark Nottingham       mnot at yahoo-inc.com