ceph: VFS: Add asynchronous fsync to ceph module, fake using synchronous call.

ceph: VFS: Add asynchronous fsync to ceph module, fake using synchronous call.

This will allow me to ultimately simplify the VFS by removing the synchronous
fsync VFS call.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13412

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Autobuild-User(master): Ralph Böhme <slow@samba.org>
Autobuild-Date(master): Mon Apr 30 21:48:55 CEST 2018 on sn-devel-144

(cherry picked from commit aefe444d17a2eee3c0ff38bd34cf9e3f012ecf51)