LU-482 test: sync new fs before first replay test

LU-482 test: sync new fs before first replay test

LVM lacks barrier support for kernel < 2.6.33, so we need to send an
explicit sync and sleep to avoid the replay_barrier call in the first
test being run from discarding blocks from just-formatted filesystems.
Otherwise this incorrectly causes just-written metadata to be lost by
the block layer by the dev-read-only failover test code.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I69fc64298603ad75a4fcda09edde5bc7ded00c1e
Reviewed-on: http://review.whamcloud.com/2223
Reviewed-by: Lai Siyao <laisiyao@whamcloud.com>
Reviewed-by: Niu Yawei <niu@whamcloud.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>