[autotest] Add some global config to support container

BUG=chromium:453624
TEST=None

Change-Id: I790030bb443ce0501d6b646311af92dd133443d6
Reviewed-on: https://chromium-review.googlesource.com/251140
Commit-Queue: Dan Shi <dshi@chromium.org>
Trybot-Ready: Dan Shi <dshi@chromium.org>
Tested-by: Dan Shi <dshi@chromium.org>
Reviewed-by: Fang Deng <fdeng@chromium.org>
diff --git a/.gitignore b/.gitignore
index 5393ca3..8b3a878 100644
--- a/.gitignore
+++ b/.gitignore
@@ -61,3 +61,6 @@
 puppylab/Vagrantfile
 puppylab/chromeos_lab_core_cluster.box
 puppylab/.vagrant
+
+# Container directory
+containers/
\ No newline at end of file