* Use `beat.name` instead of `beat.hostname` in visualizations. See elastic#5276 for
  the motivation
* Add a "tip" widget that tells user how they can select another host.
* Automatically set a search pattern of the form `beat.name: "HOSTNAME"` where
  HOSTNAME is the Beat name (hostname) that uploads the dashboards.

The way the last point works is that I saved the dashbaord using this filter:
`beat.name:"CHANGEME_HOSTNAME"`. The kibana loader code does a string replacement
and replaces `CHANGEME_HOSTNAME` with the actual hostname. The disadvantage of this
approach (vs doing JSON parsing) is that we must remember to always save that
dashboard with the `CHANGEME_HOSTNAME` wildcard in place. I have added a unit test
to the system module that checks for that, so it should be relatively hard for
us to forget.

Closes elastic#5276.