Revisit response time requirements for non-LRO operations

[mikekistler]

From this comment on #517

It would be nice to include a little more specificity into what a "significant amount of time" mean. Perhaps something like "the amount of time is call pattern specific and will vary from a service to another. However, the recommendation is for most services the P99 should complete within 10 seconds and P90 around 3 seconds." I see that we cover the numbers in the Guidelines.md file in the definition section but perhaps 1 second P99 is too stringent for most of the services?