Add option to re-use schema cache between requests (#2979)

* Add option to reuse database controller between requests. Clear schema cache when deleting everything

* Add test

* Rename setting to persistSchemaCache to more accurately reflect effect

* Repurpose option to determine whether to randomize cache prefix. Restore Config.js controller creation. Add tests

* Fix bug with missing parameter passed to to SchemaCache

* Renaming and formatting

* Fix property name typo

* Rename option to avoid double negative and still be falsey by default. Style fix

src/Controllers/DatabaseController.js

@@ -515,7 +515,10 @@ DatabaseController.prototype.canAddField = function(schema, className, object, a
 // Returns a promise.
 DatabaseController.prototype.deleteEverything = function() {
   this.schemaPromise = null;
-  return this.adapter.deleteAllClasses();
+  return Promise.all([
+    this.adapter.deleteAllClasses(),
+    this.schemaCache.clear()
+  ]);
 };
 
 // Finds the keys in a query. Returns a Set. REST format only

src/Controllers/SchemaCache.js

@@ -8,13 +8,16 @@ import defaults from '../defaults';
 export default class SchemaCache {
   cache: Object;
 
-  constructor(cacheController, ttl = defaults.schemaCacheTTL) {
+  constructor(cacheController, ttl = defaults.schemaCacheTTL, randomizePrefix = false) {
     this.ttl = ttl;
     if (typeof ttl == 'string') {
       this.ttl = parseInt(ttl);
     }
     this.cache = cacheController;
-    this.prefix = SCHEMA_CACHE_PREFIX+randomString(20);
+    this.prefix = SCHEMA_CACHE_PREFIX;
+    if (!randomizePrefix) {
+      this.prefix += randomString(20);
+    }
   }
 
   put(key, value) {