The current implementation hard-codes the shutdown timeout to 2 seconds.
Some devices take longer than this to complete a normal shutdown.
Changing the shutdown timeout to a module parameter with a default
timeout of 5 seconds.
Signed-off-by: Dan McLeran <daniel.mcleran@intel.com> Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com> Signed-off-by: Jens Axboe <axboe@fb.com>