zk: use curator 2.5.0

Curator 2.5.0 contains a PersistentEphemeralNode fix the we might have
been hitting when seeing ephemeral node split brain syndrome.

https://github.com/apache/curator/commit/bfdef2ddc1c3f2121256045690b39baafa269151
travis: Export MAVEN_OPTS in before_script

Rather than overriding script section altogether, just set MAVEN_OPTS. This
preserves any options that Travis passes to Maven by default, such as the
"-B" batch mode flag.
Merge pull request #50 from spotify/rohan/travis

travis: Export MAVEN_OPTS in before_script
Merge pull request #47 from spotify/dano/curator-2.5.0

zk: use curator 2.5.0
prepare for sonatype hosting

* Use sonatype parent pom
* Add sonatype required elements
Merge pull request #48 from spotify/dano/sonatype

prepare for sonatype hosting
Added expires field to job definition

This will be used so jobs created during integration tests
can be garbage collected by the master. It can be passed to
the CLI as an ISO-8601 string.
ExpiredJobReaper: initial implementation

Periodically poll for expired jobs, and undeploy and remove them.

This should eventually be moved out of the master into its own process.