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.

CHANGELOG.next.asciidoc

@@ -148,6 +148,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Fix metrics hints builder to avoid wrong container metadata usage when port is not exposed {pull}18979[18979]
 - Server-side TLS config now validates certificate and key are both specified {pull}19584[19584]
 - 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

@@ -305,7 +305,9 @@ 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)