hg: openjfx/9-dev/rt: 8172988: gradle :web:test should run in headless mode

[kevin.rushforth at oracle.com]

Changeset: 34574df2e46e
Author:    kcr
Date:      2017-01-19 07:49 -0800
URL:       http://hg.openjdk.java.net/openjfx/9-dev/rt/rev/34574df2e46e

8172988: gradle :web:test should run in headless mode
Reviewed-by: ddhill

! build.gradle