LU-1023 utils: Time counting fix for obdfilter-survey

LU-1023 utils: Time counting fix for obdfilter-survey

1. Assigning the start and end time of test_brw so it
   can get correct time usage.
2. In mds_survey, it adds a new output line for threas utils,
   (Total: total xxxx threads X sec ...), and we should skip
   this line in get_stats(obdfilter-survey), so it can get
   correct min/max time.

Signed-off-by: Wang Di <di.wang@whamcloud.com>
Change-Id: I58c13bde299c254ed10e1405bfed3e1dce4ef216
Reviewed-on: http://review.whamcloud.com/1999
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>