refactor: parameterize configureApp function (inject db list)

Reason: easier testing (mocking) and better readability

Note: did additional refactoring

src/app.ts

@@ -38,12 +38,11 @@ import {thingUpdateRouter} from './routes/thing-update-route';
 import {virtualPluginRoute} from './routes/virtual-plugin-route';
 import {BulkStorage} from './storage/bulk-storage';
 import {DatabaseConstructor} from './storage/database';
-import {Elasticsearch} from './storage/elasticsearch/elasticsearch';
 
 /**
  * Configure the backend
  */
-export async function configureApp(app: Express) {
+export async function configureApp(app: Express, databases: {[name: string]: DatabaseConstructor; }) {
   let integrationTestTimeout: NodeJS.Timeout;
   // request loggers have to be the first middleware to be set in express
   app.use(morgan('dev', {
@@ -59,11 +58,8 @@ export async function configureApp(app: Express) {
       }
 
       // tslint:disable-next-line: no-magic-numbers
-      if (res.statusCode < 400) {
-        return true;
-      }
+      return res.statusCode < 400;
 
-      return false;
     }, stream: process.stdout,
   }));
 
@@ -142,10 +138,6 @@ export async function configureApp(app: Express) {
       .on('end', endCallback);
   });
 
-  const databases: {[name: string]: DatabaseConstructor; } = {
-    elasticsearch: Elasticsearch,
-  };
-
   // validate config file
   await validator.addSchemas(join('node_modules', '@openstapps', 'core', 'lib', 'schema'));