LU-12766 test: convert time to seconds properly

LU-12766 test: convert time to seconds properly

According to test logs, grace time could be 3m56s,
and it will be converted to 21305s by wrongly which
caused timeout of test sytem.

Actually, grace time could be something like 1w2d3h4m5s
Fix calculations for this.

Test-Parameters: trivial testlist=sanity-quota
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Change-Id: I1c02e83f5ec15de2a4a6b312dd6e36b55dd4a7bc
Reviewed-on: https://review.whamcloud.com/41259
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>