Report errors creating peer connection in AppRTC Demo Android.

Right now if an exception is thrown, it doesn't seem to be logged
anywhere. This CL makes it show a pop-up with the error message.
This should save time debugging issues.

Review-Url: https://codereview.webrtc.org/2049933004
Cr-Commit-Position: refs/heads/master@{#13120}

webrtc/examples/androidapp/src/org/appspot/apprtc/PeerConnectionClient.java

@@ -286,8 +286,13 @@ public class PeerConnectionClient {
     executor.execute(new Runnable() {
       @Override
       public void run() {
-        createMediaConstraintsInternal();
-        createPeerConnectionInternal(renderEGLContext);
+        try {
+          createMediaConstraintsInternal();
+          createPeerConnectionInternal(renderEGLContext);
+        } catch (Exception e) {
+          reportError("Failed to create peer connection: " + e.getMessage());
+          throw e;
+        }
       }
     });
   }