Path to data in test command should be absolute and relative

[hvgazula]

@gaiborjosue quick question: Looking at the add model instructions, you said the path to data should be relative to the repo structure. But at inference time, in the zoo cmd-line, the data can be anywhere on the system. In that case, relative path will raise an error. Won't it?

https://github.com/neuronets/trained-models/blob/master/add_model_instructions.md#8-test-command