Bug: Dev guild object cache inaccessible after creation

During the create case of dev guild initialization, the representative Guild object isn't available after Bot.create_guild() is called.

We ought to Bot.wait_for() the guild_available event that the framework emits, as this indicates that it has successfully populated the cache.

Doing this will allow us to remove some follow-on API calls later in this code path e.g. Bot.fetch_guild() and Guild.fetch_channels().