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/build/Android.common_path.mk b/build/Android.common_path.mk
index b1644df..e213dc4 100644
--- a/build/Android.common_path.mk
+++ b/build/Android.common_path.mk
@@ -38,7 +38,7 @@
 ifneq ($(TMPDIR),)
 ART_HOST_TEST_DIR := $(TMPDIR)/test-art-$(shell echo $$PPID)
 else
-ART_HOST_TEST_DIR := /tmp/test-art-$(shell echo $$PPID)
+ART_HOST_TEST_DIR := /tmp/$(USER)/test-art-$(shell echo $$PPID)
 endif
 
 # core.oat location on the device.