LU-3285 tests: add dom into racer test suite

LU-3285 tests: add dom into racer test suite

Add dom into racer test and fix a problem where it checks OSTCOUNT
to decide if to use specific layout.

Test-parameters: trivial testlist=racer,racer,racer mdscount=1 mdtcount=1

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: Ie3245644589f636201d11d9fc2ce86ecec82649e
Reviewed-on: https://review.whamcloud.com/29631
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>