attestation: Use VPD cache.

BUG=chromium:783127
TEST=PreCQ passes.

Change-Id: I75a200f42bb7710e478e96c31fc02b07cc570fd8
Reviewed-on: https://chromium-review.googlesource.com/766587
Commit-Ready: Jorge Lucangeli Obes <jorgelo@chromium.org>
Tested-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Reviewed-by: Mattias Nissler <mnissler@chromium.org>
Reviewed-by: Yves Arrouye <drcrash@chromium.org>
diff --git a/attestation/server/attestationd.conf b/attestation/server/attestationd.conf
index 7321017..3adf8dd 100644
--- a/attestation/server/attestationd.conf
+++ b/attestation/server/attestationd.conf
@@ -21,7 +21,6 @@
 stop on stopping boot-services
 respawn
 
-
 # Where we store the attestation-based enterprise enrollment data. The
 # daemon will check for this environment variable and read the file at
 # startup before forking.
@@ -31,9 +30,9 @@
   # Ensure attestationd will have permissions for attestation.epb.
   chgrp preserve /mnt/stateful_partition/unencrypted/preserve
   chmod 775 /mnt/stateful_partition/unencrypted/preserve
-  (vpd -g stable_device_secret_DO_NOT_SHARE || printf '') >$ABE_DATA_FILE
+  (vpd_get_value stable_device_secret_DO_NOT_SHARE || printf '') >"${ABE_DATA_FILE}"
 end script
 
 expect fork
 exec /usr/sbin/attestationd
-post-start exec rm -f $ABE_DATA_FILE
+post-start exec rm -f "${ABE_DATA_FILE}"