Handle more gracefully adding the same testtuple twice

[jeandut]

Currently when adding the same testtuple twice the SDK raises the error:
substra.sdk.exceptions.AlreadyExists: Object with key(s) 'A' already exists.
Maybe one could catch the error and return a warning instead like: "testtupple already submitted " while returning the same dict the previous testtuple returned ?

[Samuel Lesuffleur]

To do that, you can use the option exist_ok=True when adding a testtuple (by default it's set to False). It will always return a testtuple even if it already exists. If it already exists a log warning will be emitted.

[jeandut]

Ok closing it then !