Add s3 watcher plugin.

Here is an example vars.yml file to pass in when running the newrelic role
with s3watcher enabled:

  ---
      S3_ACCESS_KEY_ID: s3accesskeyid
      S3_SECRET_ACCESS_KEY: s3secretkey
      S3_BUCKET_NAME: bucketname
      AWS_REGION: us-foo-1
      S3_CONFIG_FILENAME: fooconfigfile
      NEWRELIC_S3_WATCHER: True
      NEWRELIC_LOGWATCH: False <--not a required var, but it's True by default
      NEWRELIC_LICENSE_KEY: "my_api_key"
Merge pull request #1671 from edx/benp/new-relic-s3-plugin

new relic s3 plugin