LU-13267 tests: improve racer cleanup

LU-13267 tests: improve racer cleanup

Add RACER_MAX_CLEANUP_WAIT parameter to specify
timeout for racer cleanup to avoid long waiting in case which
racer processes went non-killable.

Loop in racer_cleanup() contains inaccuracy which made the loop
to sleep less that it was supposed to. Fix it.

Test-Parameters: trivial testlist=racer
Cray-bug-id: LUS-8498
Signed-off-by: Elena Gryaznova <elena.gryaznova@hpe.com>
Reviewed-by: Vladimir Saveliev <vladimir.saveliev@hpe.com>
Reviewed-by: Andriy Skulysh <andriy.skulysh@hpe.com>
Change-Id: I32dac8bc11ef2041a1a580054c2782780bb5980e
Reviewed-on: https://review.whamcloud.com/37638
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Andriy Skulysh <c17819@cray.com>
Reviewed-by: Vladimir Saveliev <c17830@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>