* [jvm-packages] Added libxgboost4j to CMake build
* [jvm-packages] Wired CMake build into create_jni.sh
* User newer CMake version on Travis
* Lowered CMake version constraints
* Fixed various quirks in the new CMake build
* Specified 'exec-maven-plugin' version
* Changed 'create_jni.sh' to fail on error
and also report each of the executed commands, which makes it easier
to debug.