Correct reporting for zero trees in GBM & DRF

Fix HEX-1512
Also beef up Runner to handle the "regression" flag.
A little cleanup of Arguments.java; also allow "-flag=true" and
"-flag=0" and "-flag=false" and "-flag=1", and "-flag" which means
"invert".
Correct reporting for zero trees in GBM & DRF

Fix HEX-1512
Also beef up Runner to handle the "regression" flag.
A little cleanup of Arguments.java; also allow "-flag=true" and
"-flag=0" and "-flag=false" and "-flag=1", and "-flag" which means
"invert".
Merge branch 'master' of github.com:0xdata/h2o