Added tool to build a complete Elasticsearch release.

This tool builds a release and runs several checks to make sure the
release is in a reasonable shape (smoke test). From a top level
perspective it runs the following steps:

 * clean the build environment `mvn clean`
 * check if a Java 6 JDK is available
 * run the tests with network and local
 * generates the checksums for the binary packages
 * uploads the binary packages to Amazon S3
 * runs a 'mvn deploy' to publish the maven artifacts

The script will create an intermediate branch from a given 'release
branch' updates all versions based on the version we are currently
releasing. Updates the 'pom.xml' file as well as the 'Version.java'
class. Once this is done it commits the changes and rebase with the
branch we want to release from, merges the changes from the intermediate
branch and pushes to the given remote repository including the release
tag.