fix caret_seed

[tmastny]

Caret seeds are more complicated than I thought. Here are some resources I'll need to figure it out.

• https://stackoverflow.com/a/32598959/6637133
• http://jaehyeon-kim.github.io/2015/05/Setup-Random-Seeds-on-Caret-Package.html
• https://stackoverflow.com/questions/13403427/fully-reproducible-parallel-models-using-caret

[tmastny]

Also determine if the seed is making the final oof_grab test fail.

[tmastny]

Sounds like this was a misunderstanding on my part. Max Kuhn himself clarifies here: https://stackoverflow.com/a/27987343/6637133

The seeds aren't as useful, because they aren't portable between model types. What I am really looking for is the index

model$control$index

which I can generate a few different ways with createResamples or createFolds.