vtest: use vtest_destroy_context to cleanup

struct vtest_context is about to get more complex.  Use
vtest_destroy_context so that we have a single point that does context
destruction.

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Isaac Bosompem <mrisaacb@google.com>

vtest/vtest_renderer.c

@@ -278,9 +278,7 @@ void vtest_cleanup_renderer(void)
       struct vtest_context *ctx, *tmp;
 
       LIST_FOR_EACH_ENTRY_SAFE(ctx, tmp, &renderer.active_contexts, head) {
-         virgl_renderer_context_destroy(ctx->ctx_id);
+         vtest_destroy_context(ctx);
-         util_hash_table_clear(ctx->resource_table);
-         vtest_free_context(ctx, true);
       }
       LIST_FOR_EACH_ENTRY_SAFE(ctx, tmp, &renderer.free_contexts, head) {
          vtest_free_context(ctx, true);