Adjust gcstress/debug/target timeouts for libcore.

The latest gcstress changes made vogar timeout when setting up tests,
so no test was actuall run.

Test: run-libcore-tests.sh
Change-Id: If36c793aa37941a09934f92b285db86bb3709940
diff --git a/tools/run-libcore-tests.sh b/tools/run-libcore-tests.sh
index aff009a..240d63c 100755
--- a/tools/run-libcore-tests.sh
+++ b/tools/run-libcore-tests.sh
@@ -156,7 +156,11 @@
 # Increase the timeout, as vogar cannot set individual test
 # timeout when being asked to run packages, and some tests go above
 # the default timeout.
-vogar_args="$vogar_args --timeout 480"
+if $gcstress && $debug && $device_mode; then
+  vogar_args="$vogar_args --timeout 960"
+else
+  vogar_args="$vogar_args --timeout 480"
+fi
 
 # set the toolchain to use.
 vogar_args="$vogar_args --toolchain d8 --language CUR"