LU-13004 target: use KIOV for out_handle

Convert out_handle() use use a BULK_BUF_KIOV rather than
a BULK_BUF_KVEC.

This is a step towards removed KVEC support and standardizing
on KIOV.

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I3f5b1b06183a716ba57d6f7f2a28bf5aa0f76dfe
Reviewed-on: https://review.whamcloud.com/36826
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>