ART: Make run-test temp dir consistent

We use the username as a directory component in run-test. Use the
same when driven through the Makefile.

Drop the username in run-test when TMP_DIR is set.

Test: m test-art-host-run-test
Test: art/test/run-test --host 001-HelloWorld
Change-Id: I060997ffbd80cd4da30dd6ac8d3954641de3292b
diff --git a/test/run-test b/test/run-test
index bbcd4b0..1ef5428 100755
--- a/test/run-test
+++ b/test/run-test
@@ -37,7 +37,7 @@
 if [ -z "$TMPDIR" ]; then
   tmp_dir="/tmp/$USER/${test_dir}"
 else
-  tmp_dir="${TMPDIR}/$USER/${test_dir}"
+  tmp_dir="${TMPDIR}/${test_dir}"
 fi
 checker="${progdir}/../tools/checker/checker.py"
 export JAVA="java"