feat: allow no project in client methods using storage emulator

[cojenco]

When using a storage emulator, allow no project/fake project marker in client.create_bucket() and client.list_buckets()

Alongside, this removes client-side validation and falls back to API validations. In this case, if a project is not set, instead of raising a ValueError in the client, the GCS server will return a BadRequest with message Required parameter: project

Fixes #699

[andrewsg]

Three points to make here:

I think if "storage.googleapis.com" in _get_storage_host() is a better idiom than using find().

We should avoid hardcoding strings like "storage.googleapis.com" when possible. Perhaps we should have a constant, and/or a helper function that answers the question consistently and globally of whether we are using the emulator?

Is there no way to avoid needing the client to be aware of the emulator at all? Perhaps it's the emulator that needs to change here?

[cojenco]

Thanks for the review! Updated according to your comments.

The user ask is to be able to run the same code against a storage emulator as well as the live server (without writing extra conditions or wrappers), often seen in testing.

client.create_bucket() and client.list_buckets() are the only 2 library methods that explicitly expect a project. I think it makes sense to allow these 2 methods to detect the emulator and use a fake project marker.

[WildSunLove]

LGTM; aside from the comments but I might just be missing something there.