Bug 1031890 - Vertical homescreen takes a long time to load

This is the line that I found bug 1034729 from. Before we were checking that we have a cached icon before downloading an icon, this "stamp" was a hint for the test here: https://github.com/KevinGrandon/gaia/blob/bug_1034729_vertical_fix_misnamed_test/apps/verticalhome/test/marionette/app_hosted_use_cached_icon_test.js#L73

I think we should still stamp it with that, assuming ```this.hasCachedIcon``` is true.