ZOOKEEPER-3234: Add Travis-CI configuration file

Author: Enrico Olivelli <eolivelli@apache.org>
Author: Enrico Olivelli <eolivelli@gmail.com>

Reviewers: andor@apache.org

Closes #751 from eolivelli/fix/travis and squashes the following commits:

bbfcfe5c1 [Enrico Olivelli] More memory
a9de203d5 [Enrico Olivelli] Update .travis.yml
f9fbd3aa8 [Enrico Olivelli] Add travis_wait
075f9c32f [Enrico Olivelli] Enable IPv6
85083d27b [Enrico Olivelli] Perform fsync
7ce12ff1d [Enrico Olivelli] Forkcount = 4
6607343e4 [Enrico Olivelli] Fix forkcount
043aa40bd [Enrico Olivelli] Do not force fsync and use 1 thread for tests
bf1384352 [Enrico Olivelli] ZOOKEEPER-3234: Add Travis-CI configuration file

.travis.yml

@@ -0,0 +1,24 @@
+language: java
+sudo: false
+
+cache:
+  directories:
+  - "$HOME/.m2"
+
+before_script:
+  # Add an IPv6 config - see the corresponding Travis issue
+  # https://github.com/travis-ci/travis-ci/issues/8361
+  - if [ "${TRAVIS_OS_NAME}" == "linux" ]; then 
+      sudo sh -c 'echo 0 > /proc/sys/net/ipv6/conf/all/disable_ipv6';
+      ulimit -s 1082768;
+    fi
+
+jobs:
+  include:
+  - stage: test
+    jdk: openjdk11
+    script: travis_wait 30 mvn verify -Dmaven.test.redirectTestOutputToFile=true -Dsurefire-forkcount=4
+
+branches:
+  only:
+  - master