Clean event queue after each case. (#398)

Case "Send a message to a remote endpoint should be resolved" fails
sometimes during check in test and nightly test. It's probably cased by
signaling messages for last case don't get flushed in time. This change
gives signaling server a chance to send out all messages before the
next case.

Author: jianjunz

test/unit/resources/scripts/p2p.js

@@ -105,6 +105,11 @@ describe('Unit tests for P2PClient', function() {
         'user2'), p2pclient3.connect('user3')])).to.be.fulfilled.and.notify(
         done);
     });
+    afterEach((done) => {
+      setTimeout(() => {
+        done();
+      }, 0);
+    });
     it('Publish a valid stream to remote endpoint then stop the publication should be resolved.', done => {
       p2pclient1.publish('user2', localStream).then(publication=>{
         p2pclient1.getStats('user2').then((stats)=>{
@@ -126,18 +131,18 @@ describe('Unit tests for P2PClient', function() {
         expect(p2pclient3.publish('user1', localStream)).to.be.rejected.and.notify(
           done);
       });
-    it('Send message to a remote endpoint should be resolved.', done => {
+    it('Send a message to a remote endpoint should be resolved.', done => {
       expect(p2pclient1.send('user2', 'message')).to.be.fulfilled.and.notify(
         done);
     });
     it(
-      'Send message to a remote endpoint not listed in local allowedRemoteIds should be rejected.',
+      'Send a message to a remote endpoint not listed in local allowedRemoteIds should be rejected.',
       done => {
         expect(p2pclient1.send('user3', 'message')).to.be.rejected.and.notify(
           done);
       });
     it(
-      'Send message to a remote endpoint not listed in remote allowedRemoteIds should be rejected.',
+      'Send a message to a remote endpoint not listed in remote allowedRemoteIds should be rejected.',
       done => {
         expect(p2pclient3.send('user1', 'message')).to.be.rejected.and.notify(
           done);