ssm: Add cleanup state feature

In some situations one may want to guarantee that the last steps of an
SSM are run even when the SSM is completed early or failed.

This can easily be done by making fpi_ssm_mark_completed jump to the
next cleanup stage when called (this also includes mark_failed). Due to
the mechanism, it is still possible to explicitly jump cleanup states by
using fpi_ssm_jump_to_state, including a jump to the final state in
order to skip all cleanup states.

libfprint/drivers/vfs5011.c

@@ -196,6 +196,7 @@ usb_exchange_async (FpiSsm                  *ssm,
   FpiSsm *subsm = fpi_ssm_new_full (FP_DEVICE (data->device),
                                     usbexchange_loop,
                                     data->stepcount,
+                                    data->stepcount,
                                     exchange_name);
 
   fpi_ssm_set_data (subsm, data, NULL);