LU-1017 handle -EAGAIN properly in lu_object_find_try()

LU-1017 handle -EAGAIN properly in lu_object_find_try()

htable_lookup() could return -EAGAIN for dying object, we should
handle it properly in lu_object_find_try().

Signed-off-by: Niu Yawei <niu@whamcloud.com>
Change-Id: I616928cb983d4f64a64f25b7d296b6c9bd18e4ea
Reviewed-on: http://review.whamcloud.com/2066
Tested-by: Hudson
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>