Add check-va-api helper

With this helper we are able to test if VA-API is available and usable.

It tests the ability to gather the supported configuration profiles, then it creates two surfaces and perform a few simple rendering transformations.

As part of https://phabricator.collabora.com/T12902, this helper will be useful to test if a pressure-vessel container has all the correct bits that libva requires. Also, like for the check-vdpau one, in the future we might even use this helper to show an additional entry in the s-r-s-i output.

/cc @smcv @jpwhiting