Better error message when trying to enroll with Basic license

[ycombinator]

Kibana version: 6.6.0

Elasticsearch version: 6.6.0

Server OS version: Mac OS X

Browser version: Chrome latest

Browser OS version: Mac OS X

Original install method (e.g. download page, yum, from source, etc.): 6.6.0 BC2

Describe the bug:

When attempting to enroll a beat while running the Basic license, the error message returned contains `[object Object] in it.

Steps to reproduce:

1. Install ES, Kibana, and Metricbeat with default configuration.
2. Start up ES and Kibana.
3. Run ./metricbeat enroll http://localhost:5601 foobar

Observed behavior:

The error message returned is:

Error while enrolling: Your [object Object] license does not support this API or is expired. Please upgrade your license.

Expected behavior:

The error message returned would be something like:

Error while enrolling: Your Basic license does not support this API or is expired. Please upgrade your license.

[ph]

This will need to be done on the Kibana side, beats just display what is coming from the API.

[ycombinator]

Indeed, hence the issue in the Kibana repo 😉