LU-11768 test: make at_max to take effect

LU-11768 test: make at_max to take effect

In test_6 of sanity-quota, the "at_max" won't affect
the "at_current" if there is no RPC to be sent in that
import, which still makes the following DQACQ request
to have larger timeout value and triggers watchdog.

Fixes: d8226b93 ("LU-11768 test: limit at_max to timeout in time")
Test-Parameters: trivial \
testlist=sanity-quota,sanity-quota,sanity-quota,sanity-quota,sanity-quota

Change-Id: Iccc969459647aa70da6f6ecb0d8d13a404bf8088
Signed-off-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/36431
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>