Examples: always use local storage

Some devices have storage but that's is limited enough not to be able to store all the metadata, but just a fingerprint id.

In such case we also need to use the local storage to be able to verify. Fprintd does this already, but we don't do it in the libfprint examples.

So, in in case we enroll, always save the print information to the disk, while in case we verify we try to load the print from disk if none can be found in the device.

As per this, I was wondering... Wouldn't be better to make fp_print_get_device_stored to return an enum so that we can define the type of device storage (i.e. whether is "full" or only containing an "handle")?