HADOOP-18106: Handle memory fragmentation in S3A Vectored IO. (#4445)

part of HADOOP-18103.
Handling memory fragmentation in S3A vectored IO implementation by
allocating smaller user range requested size buffers and directly
filling them from the remote S3 stream and skipping undesired
data in between ranges.
This patch also adds aborting active vectored reads when stream is
closed or unbuffer() is called.

Contributed By: Mukund Thakur
17 files changed