OutputPageTest: Don't assume Vector is the default skin

Whenever Vector is removed from core, this can be replaced with
"fallback" (or something that is shipped with core). Ideally this
test wouldn't depend upon Skin, but that's a whole different issue.

Change-Id: I76a74deb95643e0d05f4d0f7e3e8d78f0efc119c
Merge "OutputPageTest: Don't assume Vector is the default skin"