Fix ml job because of missing Datafeed in the logs

The log output from ML changed. Because of this the check on the Beats side has to be adjusted. The old check was kept in place for backward compatiblity.

```
2018-12-20T14:11:14.356ZERRORinstance/beat.go:906Exiting: 2 errors: Error setting up ML for apache2: 5 errors: [status_exception] A datafeed [datafeed-filebeat-apache2-access-visitor_rate] already exists for job [filebeat-apache2-access-visitor_rate]; [status_exception] A datafeed [datafeed-filebeat-apache2-access-response_code] already exists for job [filebeat-apache2-access-response_code]; [status_exception] A datafeed [datafeed-filebeat-apache2-access-remote_ip_url_count] already exists for job [filebeat-apache2-access-remote_ip_url_count]; [status_exception] A datafeed [datafeed-filebeat-apache2-access-low_request_rate] already exists for job [filebeat-apache2-access-low_request_rate]; [status_exception] A datafeed [datafeed-filebeat-apache2-access-remote_ip_request_rate] already exists for job [filebeat-apache2-access-remote_ip_request_rate]; Error setting up ML for nginx: 5 errors: [status_exception] A datafeed [datafeed-filebeat-nginx-access-visitor_rate] already exists for job [filebeat-nginx-access-visitor_rate]; [status_exception] A datafeed [datafeed-filebeat-nginx-access-remote_ip_url_count] already exists for job [filebeat-nginx-access-remote_ip_url_count]; [status_exception] A datafeed [datafeed-filebeat-nginx-access-response_code] already exists for job [filebeat-nginx-access-response_code]; [status_exception] A datafeed [datafeed-filebeat-nginx-access-remote_ip_request_rate] already exists for job [filebeat-nginx-access-remote_ip_request_rate]; [status_exception] A datafeed [datafeed-filebeat-nginx-access-low_request_rate] already exists for job [filebeat-nginx-access-low_request_rate]
```

filebeat/tests/system/test_ml.py

@@ -93,6 +93,9 @@ def _run_ml_test(self, setup_flag, modules_flag):
             "-c", cfgfile
         ]
 
+        # Skipping dashboard loading to speed up tests, unfortunately only works for setup and not --setup
+        cmd += ["-E", "setup.dashboards.enabled=false"]
+
         if setup_flag:
             cmd += ["--setup"]
         else:

libbeat/ml-importer/importer.go

@@ -229,7 +229,7 @@ func checkResponse(r []byte) error {
 
 	for _, feed := range resp.Datafeeds {
 		if !feed.Success {
-			if strings.HasPrefix(feed.Error.Msg, "[resource_already_exists_exception]") {
+			if strings.HasPrefix(feed.Error.Msg, "[status_exception] A datafeed") || strings.HasPrefix(feed.Error.Msg, "[resource_already_exists_exception]") {
 				logp.Debug("machine-learning", "Datafeed already exists: %s, error: %s", feed.ID, feed.Error.Msg)
 				continue
 			}