LU-2291 tests: add "lfs setstripe" to racer

LU-2291 tests: add "lfs setstripe" to racer

During the file_create.sh test, instead of just creating the file with
default striping use "lfs setstripe -c ${{RANDOM % OSTCOUNT}}" to both
exercise the "lfs setstripe" path under load, as well as make the
file IO spread across multiple OSTs.

Test-Parameters: envdefinitions=SLOW=yes testlist=racer
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I26020d516388af0bb95d320c0f2a364395bd0b12
Reviewed-on: http://review.whamcloud.com/4478
Reviewed-by: Jian Yu <jian.yu@intel.com>
Tested-by: Hudson
Reviewed-by: wangdi <di.wang@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>