Exclude /opt/google/containers for factory images

Factory images have no need for items on /opt/google/containers, so
these items need not be included in the factory image.

BUG=None
TEST=./build_image factory_install # And verify no containers items

Change-Id: I8c38187e199851baab5858ab298d6a32856c336d
Reviewed-on: https://chromium-review.googlesource.com/322896
Commit-Ready: Josh Horwich <jhorwich@chromium.org>
Tested-by: Josh Horwich <jhorwich@chromium.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
diff --git a/common.sh b/common.sh
index b3227eb..4834f4b 100644
--- a/common.sh
+++ b/common.sh
@@ -483,6 +483,7 @@
   ${DEFAULT_INSTALL_MASK}
   /opt/[^g]*
   /opt/google/chrome
+  /opt/google/containers
   /opt/google/o3d
   /opt/google/talkplugin
   /usr/lib/dri