Fix loading

[lucksus]

PR summary

Loading of instances was broken.

Two reasons why we didn't notice this right away:

1. The test for this was not really testing loading and got deactivated. Which then allowed a change to happen that broken the loading code in every case.
2. The conductor always first tries to load from the given storage. If that fails, it creates a new instance. This second branch obviously doesn't erase everything in the CAS and was ending up with a partially loaded state. Source chain was loaded correctly. Agent keys are stored in the keystore anyway. So we only missed some things, especially the holding list.

changelog

• if this is a code change that effects some consumer (e.g. zome developers) of holochain core, then it has been added to our between-release changelog with the format

- summary of change [PR#1234](https://github.com/holochain/holochain-rust/pull/1234)

documentation

• this code has been documented according to our docs checklist

[maackle]

What happens if we have a Dna in the context/state, but then call initialize with Some(dna)? If that is invalid behavior, maybe that is an argument for splitting this into two different functions so we can't do something invalid.

[lucksus]

Please have a look again. I've left it as one function for now, but added comments and a panic in case maybe_dna is Some AND there is a DNA already in the nucleus state.

[maackle]

Cool, fair enough