LU-5773 test: reduce thread count

LU-5773 test: reduce thread count

Reduce thread count for the test_1c of obdfilter-survery test to
prevent OOM on vm.

Test-Parameters: alwaysuploadlogs \
envdefinitions=SLOW=yes,ENABLE_QUOTA=yes \
mdtfilesystemtype=ldiskfs mdsfilesystemtype=ldiskfs ostfilesystemtype=ldiskfs \
mdtcount=1 testlist=obdfilter-survey,obdfilter-survey,obdfilter-survey

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Change-Id: I83926a538827dea6682bd0f84434ba5d351cfd88
Reviewed-on: http://review.whamcloud.com/13078
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>