Require sudo usage to be non-interactive.

First, add a enable_strict_sudo helpers that scripts that are
sudo strict can invoke.  This does a sanity check bailing immediately
if invoked from a non sudo-keep-alive context.

Second, update enter_chroot.sh and make_chroot.sh to be strict.

While this is strict, that's the point.  The aim of this is to block
the previous sudo interactive mess for spreading, let alone reappearing
in scripts/code that has been cleansed.

BUG=chromium-os:18393
TEST=cros_sdk --replace; in the midst of it, do sudo -k.
     cros_sdk should thus bail out w/ an appropriate error.
CQ-DEPEND=I01bb1466cf027401fa387af7fad15e42fd33aea4

Change-Id: I76c5b87a812cc78c30a2eb1a0c56b9e438f4a98f
Reviewed-on: https://gerrit.chromium.org/gerrit/15294
Commit-Ready: Brian Harring <ferringb@chromium.org>
Reviewed-by: Brian Harring <ferringb@chromium.org>
Tested-by: Brian Harring <ferringb@chromium.org>
diff --git a/sdk_lib/enter_chroot.sh b/sdk_lib/enter_chroot.sh
index 0339a76..de484af 100755
--- a/sdk_lib/enter_chroot.sh
+++ b/sdk_lib/enter_chroot.sh
@@ -9,6 +9,8 @@
 SCRIPT_ROOT=$(readlink -f $(dirname "$0")/..)
 . "${SCRIPT_ROOT}/common.sh" || exit 1
 
+enable_strict_sudo
+
 # Script must be run outside the chroot and as a regular user.
 assert_outside_chroot
 assert_not_root_user