CA-147671: Refactor block-aio.c before unit testing tdaio_queue_read()

Signed-off-by: Flavien Quesnel <flavien.quesnel@citrix.com>
CA-147671: [UnitTest] Add unit tests for tdaio_queue_read()

Signed-off-by: Flavien Quesnel <flavien.quesnel@citrix.com>