LU-746 test: obdfilter-survey FAIL hndls expected >8, have 2

LU-746 test: obdfilter-survey FAIL hndls expected >8, have 2

obdfilter-survey.sh checks jbd proc stats after survey, but it
doesn't take obd cleanup time into account, so the stats collected
may not reflect the data of test. To fix this, save run time of
survey test, and collect stats of (run_time/4) ago.

Signed-off-by: Lai Siyao <laisiyao@whamcloud.com>
Change-Id: I597a6279353c203b50b1c2b17543bd34d86d8806
Reviewed-on: http://review.whamcloud.com/1645
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Liang Zhen <liang@whamcloud.com>
Reviewed-by: Johann Lombardi <johann@whamcloud.com>