s3a to instrument duration of HTTP calls

HADOOP-13844 proposes pulling out the swift duration classes for reuse; this patch proposes instrumenting s3a with it.

One interesting question: what to do with the values. For now, they could just be printed, but it might be interesting to include in FS stats collected at the end of a run. However, those are all assumed to be simple counters where merging is a matter of addition. These are more metrics