Re-adding device with same path formats device without --force

[benengele]

Steps:

1. Add device
2. Add plots
3. Add device again
4. Repeat 3

Expected:
Warning will be issued that device is already in geometry

Actual:
Device will be re-formatted (presumably) corrupting plots already added to the device.
Inconsistent behaviour when repeated multiple times:
Warning: This looks like a PlotFS partition, but it is not registered.
Same device registered multiple times.

[benengele]

Probably caused by not unmounting the device wiping out the signature.

[szatmary]

I believe this happens when the device is formatted as a plots drive, but its id is not in the geometry file.