LU-4263 osd-zfs: Avoid converting last ID FIDs to OST IDs

LU-4263 osd-zfs: Avoid converting last ID FIDs to OST IDs

When obdfilter-survey first creates an object on a fresh ZFS OST, the
last ID object for FID_SEQ_ECHO has to be created in the first place.
The last ID FID, [FID_SEQ_ECHO:0:0], can not be converted to an OST ID
because the resulting OST ID would be indistinguishable from an
FID_SEQ_OST_MDT0 OST ID and would confuse ostid_id().  This patch
checks for last ID FIDs before converting them to OST IDs in
osd_get_idx_for_ost_obj().

Change-Id: I96cdf85b4725e4882cecabaf90466c7f77a5e0a6
Intel-bug-id: FF-182
Signed-off-by: Li Wei <wei.g.li@intel.com>
Reviewed-on: http://review.whamcloud.com/8301
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>