[CI] Enable running on the new Travis' container-based infrastructure

* Disable sudo (https://docs.travis-ci.com/user/workers/container-based-infrastructure/)

* Fix buffer overflow
    Buffer overflow in Java_java_net_Inet4AddressImpl_getLocalHostName of OpenJDK6 and OpenJDK 7 (Refs: travis-ci/travis-ci#5227). Travis container-based infrastructure does not suffer from the long hostnames.

Closes: elastic#538

Author: Kenta Suzuki

.travis.yml

@@ -33,3 +33,5 @@ install: "gem uninstall bundler -axI && gem install bundler -v 1.11.2"
 
 notifications:
   disable: true
+
+sudo: false