Sphinx manager still spawns duplicate Sphinx agents on server restart with multiple projects open

[alcarney]

The current fix has calls to get_client() wait on an asyncio.Task that is in the process of creating a new client.

This works well when a single project is open, however when a client is bulk-opening documents spanning multiple projects it's not sufficient. This is due to the client being created is only relevant for some of the documents, once the client has been created multiple documents are free to start the process of creating their own clients - leading to duplicates