LU-889 recovery: rework extend_recovery_timer()

LU-889 recovery: rework extend_recovery_timer()

Commit 8da33c6cc5192303fcd18f45892e1f115004e662 is buggy where
the time used to rearm the timer is wrong. In this patch, I
will reset all changes and use the same scheme as 2.1 release.

Signed-off-by: Jinshan Xiong <jinshan.xiong@whamcloud.com>
Change-Id: Icd887687262644e1a1cfffd6f34eacc5bc418f84
Reviewed-on: http://review.whamcloud.com/1722
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Mike Pershin <tappro@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>