Bug 1020903 - Missing splash icon when an application is hosted via https

With the way the URI was constructed before, if https was used with
default port, a.port would be empty and port 80 would wrongly be used.
Instead, we now use the origin as it is.
Merge pull request #20066 from lanker-sony/splash-icon-uri

Bug 1020903 - Missing splash icon when an application is hosted via https