enter_chroot.sh: install /root/.boto symlink for sudoed invocations

Since sudo changes $HOME to /root, sudoed invocations of gsutil/boto
won't find the necessary credentials. This solves the problem by
installing a symlink at /root/.boto to the correct credentials file,
similar to how it's done for /home/$USER/.boto.

BUG=None
TEST=/root/.boto symlink created upon entering the chroot

Change-Id: I541556f836fa5d0b9708e5604218058401563fb3
Reviewed-on: https://gerrit.chromium.org/gerrit/32430
Reviewed-by: David James <davidjames@chromium.org>
Reviewed-by: Ryan Cui <rcui@chromium.org>
Commit-Ready: Gilad Arnold <garnold@chromium.org>
Tested-by: Gilad Arnold <garnold@chromium.org>
diff --git a/sdk_lib/enter_chroot.sh b/sdk_lib/enter_chroot.sh
index 58cb0f5..8e76444 100755
--- a/sdk_lib/enter_chroot.sh
+++ b/sdk_lib/enter_chroot.sh
@@ -470,11 +470,15 @@
     fi
 
     # If the private overlays are installed, gsutil can use those credentials.
-    if [ ! -e "${FLAGS_chroot}/home/${USER}/.boto" ]; then
-      boto='src/private-overlays/chromeos-overlay/googlestorage_account.boto'
-      if [ -s "${FLAGS_trunk}/${boto}" ]; then
+    # We're also installing credentials for use by sudoed invocations.
+    boto='src/private-overlays/chromeos-overlay/googlestorage_account.boto'
+    if [ -s "${FLAGS_trunk}/${boto}" ]; then
+      if [ ! -e "${FLAGS_chroot}/home/${USER}/.boto" ]; then
         ln -s "trunk/${boto}" "${FLAGS_chroot}/home/${USER}/.boto"
       fi
+      if [ ! -e "${FLAGS_chroot}/root/.boto" ]; then
+        sudo ln -s "../home/${USER}/trunk/${boto}" "${FLAGS_chroot}/root/.boto"
+      fi
     fi
 
     # Have found a few chroots where ~/.gsutil is owned by root:root, probably