Remove the `Config#current_cluster` global variable

[WilliamMcCumstie]

This causes conflicts between the server and commander. Instead the "current_cluster" should be manually passed into ScopedCommand. This will remove the chance the two get confused.

Then somewhere in the CommanderProxy a config file could be read, or a symlink followed to the current_cluster. This means CLI commands will not need to specify the current cluster each time.