Where hgen stands for "header generator".

travis-ci: success for compel: Rename 'piegen' action into 'hgen'
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>