Use ONOS_STAGE_ROOT if defined

Change-Id: I4989e1a8e18c9a1b7172bfa941f53b4b9b76a550
diff --git a/tools/test/bin/onos-archetypes-test b/tools/test/bin/onos-archetypes-test
index 8775b11..04fe169 100755
--- a/tools/test/bin/onos-archetypes-test
+++ b/tools/test/bin/onos-archetypes-test
@@ -18,7 +18,7 @@
 
 set -e
 
-export AROOT=/tmp/foo
+export AROOT=${ONOS_STAGE_ROOT:-/tmp}/foo
 export ARCHETYPE_OPTS="-DarchetypeGroupId=org.onosproject -DarchetypeVersion=1.5.0-SNAPSHOT"
 
 mkdir -p $AROOT