LU-2523 mdt: handle -ENOENT && !MDS_OPEN_CREAT in reint open

LU-2523 mdt: handle -ENOENT && !MDS_OPEN_CREAT in reint open

If mdt_open_by_fid_lock() returns -ENOENT and MDS_OPEN_CREAT is not
set in create flags then bail out and return -ENOENT from
mdt_reint_open().  In mdt_open_by_fid_lock() if -ENOENT is returned
then ensure that DISP_IT_EXECD is set in the reply disposition.  Add
sanity test_27B to call the LL_IOC_LOV_SETSTRIPE ioctl() on an open
unlinked file, a situation which triggers the first case.  In sanityn
test 30, remote the requirement that opening an unlinked file via
/proc/PID/exe return -ESTALE.  In racer's file_create.sh, reinstate
the call to 'lfs setstripe' before dd is started, effectively
reverting commit 0be1c87fe2d4ffddaca9e568cc137518b7368b2d.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I74e2297c4210ff18acbf60efdf51049d9a88cbea
Reviewed-on: http://review.whamcloud.com/5417
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Tested-by: Hudson
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>