HADOOP-13551. AWS metrics wire-up (#2778)


Moves to the builder API for AWS S3 client creation, and
offers a similar style of API to the S3A FileSystem and tests, hiding
the details of which options are client, which are in AWS Conf,
and doing the wiring up of S3A statistics interfaces to the AWS
SDK internals. S3A Statistics, including IOStatistics, should now
count throttling events handled in the AWS SDK itself.

This patch restores endpoint determination by probes to US-East-1
if the client isn't configured with fs.s3a.endpoint.

Explicitly setting the endpoint will save the cost of these probe
HTTP requests.

Contributed by Steve Loughran.
11 files changed