open-configuration needs to be customizable

[lamoni]

In planning for Ephemeral Databases, I need to add an argument to openConfiguration() to allow either setting "private", or a custom ephemeral database name.

E.g.

<rpc>
  <open-configuration>
    <ephemeral-instance>name-of-the-instance</ephemeral-instance>
  </open-configuration>
</rpc>