Newrelic plugins

Description of your patch
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**Due to the Python requirements, this is only compatible with new Gentoo stack**

This installs the [MeetMe newrelic_plugin_agent](https://github.com/MeetMe/newrelic-plugin-agent) on Engine Yard environments. Users can use the base recipe and customize based on which plugins need to be enabled.

Estimated risk
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Low

Components involved
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- Installs `pip` with `easy_install`
- Uses `pip` to install `newrelic-plugin-agent`
- Adds configuration file to `/etc`
- Creates init.d script and adds newrelic_plugin_agent to the default run level
- Uses monit to monitor the service

Description of testing done
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- Tested locally with chefspec and foodcritic
- Uploaded and applied recipes to solo and cluster, stable-v4 environments

QA Instructions
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1. Make sure New Relic is enabled
2. Add license key to `newrelic_plugins/recipes/default.rb`
3. Uncomment 'redis' section in `newrelic_plugins/templates/default/newrelic_plugin_agent.yml` file
4. Include the recipe in the main recipe
5. Upload and apply to environment
6. Verify that files are in place, daemon is running, and Redis shows up in New Relic dash. Can also use `redis-cli` to verify that data is going into New Relic