Improve Beats + Logstash getting started steps

[dedemorton]

Feedback from Walter Rafelsberger regarding the metricbeat gs docs:
Have some feedback regarding the metricbeat setup documentation. Here’s what I noticed:
If you want to use beats with logstash, you have to disable the Elasticsearch endpoint in the configuration (https://www.elastic.co/guide/en/beats/metricbeat/master/logstash-output.html).
However, then in a later step, configuring the Kibana dashboards (./metricbeat setup —dashboards here: https://www.elastic.co/guide/en/beats/metricbeat/master/load-kibana-dashboards.html) fails because it still requires the elasticsearch endpoint.
So to make it work I had to revert the changes in the config back and forth regarding the logstash output.

• Document how to enable/disable by using enabled: false instead of commenting it out.
• Might also mention using -E "output.elasticsearch.hosts=["http://localhost:9200"]" to override the setting at the command line so the user doesn't have to change the config file.

[dedemorton]

The getting started docs now describe what to do if you are using LS output and want to set up dashboards and other assets, so I'm closing this.