Initial the Maven project management for logstash

1. Created the pom.xml for logstash with adding the jruby-complete jar as
   the dependence, which can be downloaded from the maven repository.
2. Added the local gem mirror: ruby.taobao.org.
3. Move the jruby gem/bundle dependences lib from the project folder to
   the home .jruby folder which can be shared with all jruby projects.

Signed-off-by: Wei Zhang <weiz@logstream.net>