Add support for http auth

[myoung34]

Resolves #16

Redaction necesary, or user/pass shows up in log. After redacting:

/aws/lambda/cloudwatch_logs_to_elasticsearch 2017/09/26/[$LATEST]cde5dc28309c4228b2b265c1cea26e9f 2017-09-26T18:12:08.322Z      35574970-a2e6-11e7-a601-6df19095e394    Running 5 handlers with _config: { elasticsearch:
   { host: 'https://es.redact.com:9200',
     httpAuth: '*****',
     index: 'logstash-2017-09-26',
     type: 'test' },
  data: 'snip',
  type: 'CloudWatch',
  processors: [ 'formatCloudwatchLogs', 'shipElasticsearch' ] }

[coveralls]

Coverage remained the same at 100.0% when pulling e82dae6 on myoung34:master into 729f9ba on arithmetric:master.

[coveralls]

Coverage decreased (-89.8%) to 10.169% when pulling 305d38f on myoung34:master into 729f9ba on arithmetric:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 371f06a on myoung34:master into 729f9ba on arithmetric:master.

[coveralls]

Coverage remained the same at 100.0% when pulling d2df96b on myoung34:master into 729f9ba on arithmetric:master.

[coveralls]

Coverage remained the same at 100.0% when pulling d2df96b on myoung34:master into 729f9ba on arithmetric:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 0566dfd on myoung34:master into 729f9ba on arithmetric:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 966fcc2 on myoung34:master into 729f9ba on arithmetric:master.

[coveralls]

Coverage remained the same at 100.0% when pulling d11b3d0 on myoung34:master into 729f9ba on arithmetric:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 5c028d1 on myoung34:master into 729f9ba on arithmetric:master.

[coveralls]

Coverage decreased (-7.4%) to 92.642% when pulling cbbf374 on myoung34:master into 729f9ba on arithmetric:master.

[myoung34]

This got noisy, opening new PR