Don't swallow Kibana index pattern errors (elastic#20121)

While running 'beat setup --dashboads' any errors that occur while importing the generated Kibana index pattern or silently ignored.
This changes that by causing the dashboard setup to stop and return the error. Dashboards won't work without the index pattern anyways.

(cherry picked from commit 7a7279f)

CHANGELOG.next.asciidoc

@@ -90,6 +90,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Fix Elasticsearch license endpoint URL referenced in error message. {issue}17880[17880] {pull}18030[18030]
 - Change `decode_json_fields` processor, to merge parsed json objects with existing objects in the event instead of fully replacing them. {pull}17958[17958]
 - Fix seccomp policy for calls to `chmod` and `chown`. {pull}20054[20054]
+- Output errors when Kibana index pattern setup fails. {pull}20121[20121]
 
 *Auditbeat*
 

libbeat/dashboards/importer.go

@@ -300,7 +300,9 @@ func (imp Importer) ImportKibanaDir(dir string) error {
 
 	// Loads the internal index pattern
 	if imp.fields != nil {
-		imp.loader.ImportIndex(imp.fields)
+		if err = imp.loader.ImportIndex(imp.fields); err != nil {
+			return errw.Wrap(err, "failed to import Kibana index pattern")
+		}
 	}
 
 	dir = path.Join(dir, versionPath)