Bug 632954 - Explicitly set NEED_XVFB to false if need-xvfb isn't set; r=tomprince

test-linux.sh defaults to true for NEED_XVFB, while build-linux.sh
defaults to false. If we are using test-linux.sh from mozharness (rather
than mozharness-test), we need to explicitly set NEED_XVFB to false in
order to not use xvfb.

Differential Revision: https://phabricator.services.mozilla.com/D22820

--HG--
extra : source : 53d3443e55d95af494d6c8bdc3d2d7a52c5eff1e

taskcluster/taskgraph/transforms/job/mozharness.py

@@ -210,6 +210,8 @@ def mozharness_on_docker_worker_setup(config, job, taskdesc):
     # Xvfb
     if run['need-xvfb']:
         env['NEED_XVFB'] = 'true'
+    else:
+        env['NEED_XVFB'] = 'false'
 
     if run['tooltool-downloads']:
         internal = run['tooltool-downloads'] == 'internal'