1) When bootstrapping a node that has the same uuid as an existing node, we currently replace them, which can lead to pretty hairy and difficult-to-debug situations. We will now use ImportUUIDBehavior.IMPORT_UUID_COLLISION_THROW to avoid these.

Note that we still delete existing node with the same path before bootstrapping.

2) Importing in a non-existent repository should not be allowed anymore. (With the ModuleVersionHandler, one can be much more flexible and deterministic in how a module is installed and bootstrapped)