prometheus editor: variable autocomplete support (PR #9988)

* prometheus ace editor, template variable support

* minor fix

* support [[var]] notation

* don't remove last ] if token type is string

* Revert "don't remove last ] if token type is string"

This reverts commit bce5b2d56e.

* Revert "support [[var]] notation"

This reverts commit 10012f8ffe.

* fix token type and regex

public/app/plugins/datasource/prometheus/query_ctrl.ts

@@ -43,7 +43,7 @@ class PrometheusQueryCtrl extends QueryCtrl {
   }
 
   getCompleter(query) {
-    return new PromCompleter(this.datasource);
+    return new PromCompleter(this.datasource, this.templateSrv);
   }
 
   getDefaultFormat() {