Update bootstrap.sh

bootstrap.sh

@@ -16,6 +16,9 @@ _builder_prepare() {
 	touch /builder/reference || exit 1
 	chown --reference "${REFERENCE}" /builder/reference || exit 1
 	chown -R builder:builder /builds/* || exit 1
+	export XVFBARGS="-screen 0 1280x1024x24"
+    export DISPLAY=:99
+    /etc/init.d/xvfb start
 }
 
 # Terminate