Add a ci_noatime bit to struct cl_io. In ll_io_init() set this bit if
O_NOATIME is set in f_flags. Ensure that this bit is propagated down
to lower layers. In osc_io_read_start() don't update atime if this bit
is set. Add sanity test 39n to check that passing O_NOATIME to open()
is honored.