virgl/ci: Add support for dEQP vtest

Provide the 'virpipe-on-gl' job for running dEQP GL tests on virpipe/vtest.

The rationale is to help reducing the regressions in Virglrenderer CI due to sharing the Mesa CI infrastructure.

Signed-off-by: Cristian Ciocaltea cristian.ciocaltea@collabora.com