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
5be450393c