Also start gl tests in vcldemo:
    $ SAL_FORCEGL=1 vcldemo --gltests

Change-Id: I8f0022770d57cd60c830659e3f7fcc0721320a10
Reviewed-on: https://gerrit.libreoffice.org/18132Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>