LU-7132 osd-ldiskfs: speedup rewrites

LU-7132 osd-ldiskfs: speedup rewrites

This patch slightly speeds up rewrites on OST
by replacing bmap calls with fiemap calls.

This patch also includes a fiemap deadlock fix
created by Alexey Lyashkov.

Change-Id: I8af6350a0049a14a3e29304087064ecdffc1be89
Signed-off-by: Andrew Perepechko <andrew.perepechko@seagate.com>
Signed-off-by: Alexey Lyashkov <alexey.lyashkov@seagate.com>
Reviewed-by: Artem Blagodarenko <artem.blagodarenko@seagate.com>
Reviewed-by: Alexander Zarochentsev <alexander.zarochentsev@seagate.com>
Xyratex-bug-id: MRP-2559
Xyratex-bug-id: MRP-2688
Reviewed-on: http://review.whamcloud.com/16360
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>