Code review comment for lp:~andreserl/maas/maas_set_correct_file_permissions

In src/provisioningserver/pxe/install_image.py, the chmod is unnecessarily being done in the critical section that we want to keep as brief as possible. Do it before, not during!

In src/provisioningserver/utils.py, the comment says we "assume" that 'filename' is not a file -- right after the "if not os.is_file(filename) that actually proves it. Can you find a better way to word that?