Make the output path configurable at runtime.

[ghoseb]

Currently the output path is guessed from the name of the fold-var. While this works fine in development, in production it's better to be able to specify the output path explicitly.

To find the output path, we check the following things in order:

• Check meta key :tesser.hadoop/output-path on the fold-var
• Check Hadoop config for key tesser.output.path
• Finally fall back to using the fold-var's name

[aphyr]

I feel like this might be better as an explicit option map instead of metadata, but metadata is only about as evil as relying on the var name itself, so I'll allow it. ;-)

[ghoseb]

I agree! Thanks! :-) :+1: