[jvm-packages] scripts to cross-build and deploy artifacts to github (#3276)

* add back train method but mark as deprecated

* add back train method but mark as deprecated

* fix scalastyle error

* fix scalastyle error

* cross building files

* update

* build with docker

* remove

* temp

* update build script

* update pom

* update

* update version

* upload build

* fix path

* update README.md

* fix compiler version to 4.8.5

jvm-packages/dev/build-docker.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+
+set -x
+
+sudo docker run --rm -m 4g -e JAVA_OPTS='-Xmx6g' --attach stdin --attach stdout --attach stderr --volume `pwd`/../:/xgboost codingcat/xgboost:latest /xgboost/jvm-packages/dev/build.sh

jvm-packages/dev/build.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+
+set -e
+
+apt-get update
+apt-get -y install g++-4.8
+apt-get -y install git openjdk-8-jdk maven python cmake
+update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.8 50
+
+export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64
+export CXX=g++
+export MAVEN_OPTS="-Xmx3000m"
+
+# build xgboost
+cd /xgboost/jvm-packages;mvn package
+