This removes a cyclical dependency when importing client/structs from
dependencies of the plugin_loader, specifically, drivers. Due to
client/config also depending on the plugin_loader.
It also better reflects the ownership of fingerprint structs, as they
are fairly internal to the fingerprint manager.
Breaking change: Added ID() to Fingerprint interface. This allows us to assign
each fingerprint implementation a unique ID, identify which fingerprinters have
been run, and also self-identify in log messages.
- Added storage fingerprinter for Windows and *nix
- Added storage tests under storage_test.go
- Added test helper functions under fingerprint/fingerprint_test.go
- Added ID() to existing finterprinters and drivers
- Added Fingerprint.ID() to log messages via log.SetPrefix()
