Bug 1646763 - sanity check that the generated HPKPStaticPins header isn't truncated. r=sfraser

It looks like genHPKPStaticPins.js can fail and still exit 0, so try and
make sure its output is plausible.  The last thing it writes is the
expiration time, so check that it's there, which should mean everything
else got generated as well.

Differential Revision: https://phabricator.services.mozilla.com/D80206

taskcluster/docker/periodic-updates/scripts/periodic_file_updates.sh

@@ -253,6 +253,10 @@ function compare_hpkp_files {
     echo "${HPKP_PRELOAD_OUTPUT} is empty. That's less good." >&2
     exit 52
   fi
+  if ! grep kPreloadPKPinsExpirationTime "${HPKP_PRELOAD_OUTPUT}"; then
+    echo "${HPKP_PRELOAD_OUTPUT} is missing an expiration time. Truncated?" >&2
+    exit 53
+  fi
   cd "${BASEDIR}"
 
   echo "INFO: diffing old/new HPKP preload lists..."