LU-14658 tests: fix conf-sanity 122b test

LU-14658 tests: fix conf-sanity 122b test

Sometimes the test 122b failed with:
dd: failed to open '/mnt/lustre/d122b.conf-sanity/f122b.conf-sanity':
Numerical result out of range

ZFS readonly simulation produces OS_STATFS_READONLY flag.
It leads to zero stripe_count at lod_get_stripe_count(), and
lod_qos_prep_create() returns -34(ERANGE).

The patch fixes it by file creation before replay_barrier.

Test-Parameters: trivial fstype=zfs env=ONLY=122b,ONLY_REPEAT=20 testlist=conf-sanity
Fixes: 747fed818be5 ("LU-14598 ofd: fix for IDIF sequence at ofd_preprw_write")
Signed-off-by: Alexander Boyko <alexander.boyko@hpe.com>
Change-Id: I7ec04ffe09d0038bcf99e1a571f14d2bfb6a5df5
Reviewed-on: https://review.whamcloud.com/45841
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Artem Blagodarenko <artem.blagodarenko@hpe.com>
Reviewed-by: Elena Gryaznova <elena.gryaznova@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>