VAO support is present, so this is just enabling the necessary testing.

The tests being skipped are being worked on with issue 3193, which is
adding support for integer values.

Bug: angleproject:3207
Test: VertexAttributeTest end2end tests
Change-Id: Ic0bbcc0e05673aece203e93d8765ac8e90dc6a59
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1672445Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Tim Van Patten <timvp@google.com>