Disable auth validation on harmony client

[frankinspace]

By default the Harmony client will validate EDL credentials when the Client object is initialized. Because bignbit creates many Harmony clients, this can lead to a lot of unnecessary network traffic and load placed on EDL endpoints.

There is an option to disable credential validation when initializing a harmony client, should_validate_auth can be set to False.

Additionally the Harmony client could be made a global variable to that lambda is able to cache the object and re-use it for multiple executions of the lambdas that interact with the harmony API.