[jvm-packages] Another pack of build/CI improvements (#2422)

* [jvm-packages] Fixed compilation on Windows

* [jvm-packages] Build the JNI bindings on Appveyor

* [jvm-packages] Build & test on OS X

* [jvm-packages] Re-applied the CMake build changes reverted by #2395

* Fixed Appveyor JVM build

* Muted Maven on Travis

* Don't link with libawt

* "linux2"->"linux"

Python2.x and 3.X use slightly different values for ``sys.platform``.

tests/travis/run_test.sh

@@ -81,10 +81,9 @@ fi
 
 if [ ${TASK} == "java_test" ]; then
     set -e
-    make jvm-packages
     cd jvm-packages
-    mvn clean install -DskipTests=true
-    mvn test
+    mvn -q clean install -DskipTests -Dmaven.test.skip
+    mvn -q test
 fi
 
 if [ ${TASK} == "cmake_test" ]; then