HEX-1781: Use covtype for imbalanced vs balanced test for GBM.
HEX-1781: Use covtype for imbalanced vs balanced test for SpeeDRF.
HEX-1781: Use covtype for imbalanced vs balanced test for DRF.
HEX-1781: Add 10% extra tolerance for DL imbalance test (just like for DRF/SpeeDRF).
Merge branch 'master' of https://github.com/0xdata/h2o