EX-2988 lipe: double confirm atime before detach it

EX-2988 lipe: double confirm atime before detach it

For lpcc_purge, double confirm the atime before detach it.
If the atime has been changed, don't detach it.

Change-Id: Ib08fc684f1c815cc8477bd8041e007541c18b6c4
Signed-off-by: Lei Feng <flei@whamcloud.com>
Test-Parameters: trivial
Reviewed-on: https://review.whamcloud.com/43312
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>