Change sleep to nanosleep to avoid failures.

The sleep function on arm 32 has points at which an unwind will fail since
the exidx information does not cover every possible pc. The nanosleep
function doesn't have this problem, it should unwind at all points.

Bug: 80314302

Test: Ran 137-cfi on target many times.
Change-Id: I6cdb8632a4e45f4cdd50f4c51a4f904eb5d2d340