LU-3270 statahead: race in start/stop statahead

LU-3270 statahead: race in start/stop statahead

When starting statahead thread, it should check whether current
lli_opendir_key was deauthorized in the mean time by another
process.

Signed-off-by: Lai Siyao <lai.siyao@intel.com>
Change-Id: I5bc00ddd1a501b94cdfe7509ddb0e7d922bef624
Reviewed-on: http://review.whamcloud.com/9666
Tested-by: Jenkins
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>