Put Travis before_install into separate script.

ci/before_install.sh

@@ -0,0 +1,7 @@
+#!/bin/sh
+
+sudo apt-get update -qq
+sudo apt-get install -qq openjdk-7-jdk openjdk-7-jre
+
+before_install="${TRAVIS_BUILD_DIR}/ci/before_install_${BACKEND}.sh"
+[ -x ${before_install} ] && ${before_install} || echo "nothing to run"