This is the API and implementation classes of HADOOP-16830,
which allows callers to query IO object instances
(filesystems, streams, remote iterators, ...) and other classes
for statistics on their I/O Usage: operation count and min/max/mean
durations.

New Packages

org.apache.hadoop.fs.statistics.
  Public API, including:
    IOStatisticsSource
    IOStatistics
    IOStatisticsSnapshot (seralizable to java objects and json)
    +helper classes for logging and integration
    BufferedIOStatisticsInputStream
       implements IOStatisticsSource and StreamCapabilities
     BufferedIOStatisticsOutputStream
       implements IOStatisticsSource, Syncable and StreamCapabilities

org.apache.hadoop.fs.statistics.impl
  Implementation classes for internal use.

org.apache.hadoop.util.functional
  functional programming support for RemoteIterators and
  other operations which raise IOEs; all wrapper classes
  implement and propagate IOStatisticsSource

Contributed by Steve Loughran.

Change-Id: If56e8db2981613ff689c39239135e44feb25f78e

…ics. (apache#2579)

Part of the HADOOP-16830 IOStatistics API feature.

If the source FileSystem's listing RemoteIterators
implement IOStatisticsSource, these are collected and served through
the IOStatisticsSource API. If they are not: getIOStatistics() returns
null.

Only the listing statistics are collected; FileSystem.globStatus() doesn't
provide any, so IO use there is not included in the aggregate results.

Contributed by Steve Loughran.

Change-Id: Iff1485297c2c7e181b54eaf1d2c4f80faeee7cfa

S3A connector to support the IOStatistics API of HADOOP-16830,

This is a major rework of the S3A Statistics collection to

* Embrace the IOStatistics APIs
* Move from direct references of S3AInstrumention statistics
  collectors to interface/implementation classes in new packages.
* Ubiquitous support of IOStatistics, including:
  S3AFileSystem, input and output streams, RemoteIterator instances
  provided in list calls.
* Adoption of new statistic names from hadoop-common

Regarding statistic collection, as well as all existing
statistics, the connector now records min/max/mean durations
of HTTP GET and HEAD requests, and those of LIST operations.

Contributed by Steve Loughran.

Change-Id: I182d34b6ac39e017a8b4a221dad8e930882b39cf