vfs_glusterfs: Return fake fd from pipe() during open

vfs_glusterfs: Return fake fd from pipe() during open

GlusterFS currently doesn't have an API implementation to set flags on
open file descriptor. Thus we use pipe() to provide valid file descriptor
from the system.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14241

Signed-off-by: Anoop C S <anoopcs@redhat.com>
Reviewed-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Guenther Deschner <gd@samba.org>
Autobuild-User(master): Günther Deschner <gd@samba.org>
Autobuild-Date(master): Fri Jan 17 17:14:43 UTC 2020 on sn-devel-184