LU-1195 llite: error handling for statahead/AGL start failure

Statahead/AGL status will be checked when release ll_statahead_info.
But if some reasons cause statahead/AGL cannot be started, then the
status are undefined. So need proper error handling for such failure
cases.

Signed-off-by: Fan Yong <yong.fan@whamcloud.com>
Change-Id: I4dec58862ad425c19e9c6284b7183b8bcaa449f6
Reviewed-on: http://review.whamcloud.com/2268
Reviewed-by: Bobi Jam <bobijam@whamcloud.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@whamcloud.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>