Support installation development dependencies

[joshuaspence]

I am currently writing RSpec tests for our Logstash configuration which will be executed with /opt/logstash/bin/rspec /path/to/spec.rb. Currently this Puppet module does not support the installation of Logstash's development dependencies, which are required in order to be able to use /opt/logstash/bin/rspec. Without the development dependencies, /opt/logstash/bin/rspec throws an error:

josh@ip-10-144-185-115:~$ /opt/logstash/bin/rspec --version
Bundler::GemNotFound: Could not find rake-11.2.2 in any of the sources
      materialize at /opt/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/spec_set.rb:92
             map! at org/jruby/RubyArray.java:2446
      materialize at /opt/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/spec_set.rb:85
            specs at /opt/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/definition.rb:132
        specs_for at /opt/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/definition.rb:177
  requested_specs at /opt/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/definition.rb:166
  requested_specs at /opt/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/environment.rb:18
            setup at /opt/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/runtime.rb:13
            setup at /opt/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler.rb:122
           setup! at /opt/logstash/lib/bootstrap/bundler.rb:64
           (root) at /opt/logstash/lib/bootstrap/rspec.rb:3

Currently I am doing this in order to install the development dependencies:

  exec { "${logstash::installpath}/bin/logstash-plugin install --development":
    unless => "${logstash::installpath}/bin/rspec --version",
  }

[joshuaspence]

See also elastic/logstash#5633.