Flag to DRF2 for building everything on one node

Default is based on whether or not the data fits on one node (very crude
notion of "fits"), but should "by default" run one node for small data.
Does not use a whole ton of one-node optimizations; does not run
tree-building on other nodes
Change copy_data to build_tree_per_node
Keep all CM's ever scored

So display can (eventually) show the CM for older & newer models
Fix GBM & DRF reporting on test sets

Was completely fubar'd.  Was using the class distribution from scoring
the validation set, then passing it thru the model's internal score
code.  For DRF this was mostly a wash; but for GBM you get an extra
Math.exp() pass...
Minor fix for tie-breaking.  Would only pick amongst N-1 choices (never
taking the last choice).  For a 2-way tie, you'd always pick #0.
Happens alot when doing an initial score with zero trees.
merge
Remove print from bad merge
Merge branch 'master' of github.com:0xdata/h2o
Turn off accidental test
Change in tie-breaking changes tiny-test results