Allow restoring acquisition and used counter state

At the moment, all existing instances are deleted when taskscaler is first initialized.

This introduces a mechanism so this can be user controlled.

The instance up function can be used both for initial preparation and for preexisting instances (the Cause for the instance existing is passed). An error returned will ultimately delete the instance. State (used count etc.) can be returned to be restored.

This might not be the best way to do this, but it's a smaller iteration in the right direction, and this is currently blocking progress.