LU-13550 osd-zfs: snapshot with incompatible clients

LU-13550 osd-zfs: snapshot with incompatible clients

snapshot_create fails when clients are connected that do not support
barrier requests.

Log some information to help the administrator track down the
connections blocking snapshot_create from succeeding.

Test-Parameters: fstype=zfs
Signed-off-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Change-Id: Ia59ea3c4c1a885e2591464cd4f8f77a1071b4786
Reviewed-on: https://review.whamcloud.com/38593
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Emoly Liu <emoly@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>