worker: Clean up rmtree logging
worker: Clean up rmtree logging

The old logging implied a bug when there wasn't one. This make things
a little more clear.

Signed-off-by: Andy Doan <09032574f02f3d5e4e489a718b8705f28c474e94@linaro.org>

linaro-technologies/jobserv,linaro-technologies/jobserv