affile: file destination flags fixed

O_APPEND was missing from open DW_REOPEN_FLAGS

Signed-off-by: Budai Laszlo <lbudai@balabit.hu>
affile: Rename __set_fd_permission() to _set_fd_permission()

Signed-off-by: Budai Laszlo <lbudai@balabit.hu>
Signed-off-by: Gergely Nagy <algernon@balabit.hu>
affile: test_affile_open added