automated/linux/piglit: Make usage of XvFB optional

Piglit tests can fail when use framebuffer to execute, so don't use
xvfb by default.

Change-Id: Idd7d7d9d496084424e44e35c81f522233d6a551c
Signed-off-by: Aníbal Limón <anibal.limon@linaro.org>
diff --git a/automated/linux/piglit/piglit.yaml b/automated/linux/piglit/piglit.yaml
index b7c41d9..476808c 100644
--- a/automated/linux/piglit/piglit.yaml
+++ b/automated/linux/piglit/piglit.yaml
@@ -24,13 +24,19 @@
     PIGLIT_SOURCE_DIR: "/usr/lib64/piglit"
     OPTIONS: "-x streaming-texture-leak -x glx"
     SUITE: "tests/quick.py"
+    USE_XVFB: "False"
 
 run:
     steps:
         - . ./automated/lib/sh-test-lib
-        - install_deps piglit xvfb
-        - export DISPLAY=:9
-        - Xvfb ${DISPLAY} -screen 0 1920x1080x24 &
+        - install_deps piglit
+        - if [ "${USE_XVFB}" = "True" ]; then
+        -     install_deps xvfb
+        -     export DISPLAY=:9
+        -     Xvfb ${DISPLAY} -screen 0 1920x1080x24 &
+        - else
+        -     export DISPLAY=${DISPLAY}
+        - fi
         - export PIGLIT_SOURCE_DIR=${PIGLIT_SOURCE_DIR}
         - cd ./automated/linux/piglit
         - piglit run ${OPTIONS} ${PIGLIT_SOURCE_DIR}/${SUITE} ./results