Adding bootstrap gem to the gem home

I have added the `bootstrap` dependencies to the `gem_path` you can now run the tests for all the plugins
using the logstash wrapper. 
```
$ ./bin/logstash rspec vendor/plugins/jruby/1.9/gems/logstash-*/spec/{input,output,filter,codec}s/*_spec.rb --order rand
```
I have tested building the tarballs and running logstash from it with success.

Fixes #2195