Clear MUC disco after closing a room

This is to avoid having a stale/inaccurate MUC features list when
reopening a previously closed MUC

src/converse-muc.js

@@ -304,6 +304,10 @@
                      */
                     this.occupants.browserStorage._clear();
                     this.occupants.reset();
+                    const disco_entity = _converse.disco_entities.get(this.get('jid'));
+                    if (disco_entity) {
+                        disco_entity.destroy();
+                    }
                     if (_converse.connection.connected) {
                         this.sendUnavailablePresence(exit_msg);
                     }

tests/utils.js

@@ -130,13 +130,12 @@
 
         return _converse.api.rooms.open(room_jid).then(() => {
             view = _converse.chatboxviews.get(room_jid);
-            if (!_converse.disco_entities.get(room_jid)) {
-                utils.waitUntil(() => _.get(_.filter(
+            return utils.waitUntil(() => _.get(_.filter(
                 stanzas,
                 iq => iq.nodeTree.querySelector(
                     `iq[to="${room_jid}"] query[xmlns="http://jabber.org/protocol/disco#info"]`
-                    )).pop(), 'nodeTree'))
-                .then(stanza => {
+                )).pop(), 'nodeTree'));
+        }).then(stanza => {
             const features_stanza = $iq({
                 'from': room_jid,
                 'id': stanza.getAttribute('id'),
@@ -164,8 +163,6 @@
                     .c('field', {'type':'text-single', 'var':'muc#roominfo_occupants', 'label':'Number of occupants'})
                         .c('value').t(0);
             _converse.connection._dataRecv(utils.createRequest(features_stanza));
-                });
-            }
             return utils.waitUntil(() => _.filter(
                     stanzas,
                     s => sizzle(`iq[to="${room_jid}"] query[node="x-roomuser-item"]`, s.nodeTree).length