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.
Change the unit test to only test if the consul link exists, not the
value of the link. The old test was hostname specific and therefore
would always be different based on the environment running the tests.
Reduce future confusion by introducing a minor version that is gossiped out
via the `mvn` Serf tag (Minor Version Number, `vsn` is already being used for
to communicate `Major Version Number`).
Background: hashicorp/consul/issues/1346#issuecomment-151663152
