Merge pull request #298 from airbnb/tibi-scala_2_12

Build aerosolve using Scala 2.12

update to spark 2.3 and scala 2.11

upgrade to spark 2.3 and scala 2.11

Add more debug info in exception

make loss configurable

Add xgboost scoring option without updating Hive tables

fix crash when config path is not exists

Allow change XGBoost obj function

Pick correct FS from path: IF default FS is different than the FS in …

…the path, pick the FS in the path

Fix typo in airlearner-strategy