[HWKMETRICS-721] Update the order of metric updates to ensure the met…

…rics is persisted on the metrics index prior to updating the tags. This will resolve corner cases where an update fails and the tags of a metric are persisted without the metric definition properly persisted.

core/metrics-core-service/src/main/java/org/hawkular/metrics/core/service/MetricsServiceImpl.java

@@ -615,7 +615,7 @@ public Observable<Void> addTags(Metric<?> metric, Map<String, String> tags) {
 
         this.updateMetricExpiration(metric.getMetricId());
 
-        return dataAccess.addTags(metric, tags).mergeWith(dataAccess.insertIntoMetricsTagsIndex(metric, tags))
+        return dataAccess.insertIntoMetricsTagsIndex(metric, tags).concatWith(dataAccess.addTags(metric, tags))
                 .toList().map(l -> null);
     }