Make db archival return a meaningful result code

This helps with automating to know when it's done. Update our own
post-test-hook to use it.

Change-Id: I61c3b187edab3e0e612470735eecd2db59028413

tools/hooks/post_test_hook.sh

@@ -6,9 +6,13 @@ function archive_deleted_rows {
     # NOTE(danms): Run this a few times to make sure that we end
     # up with nothing more to archive
     for i in `seq 30`; do
-        out=$($MANAGE db archive_deleted_rows --verbose --max_rows 1000)
-        echo $?
-        if [[ $out =~ "Nothing was archived" ]]; then
+        $MANAGE db archive_deleted_rows --verbose --max_rows 1000
+        RET=$?
+        if [[ $RET -gt 1 ]]; then
+            echo Archiving failed with result $RET
+            return $RET
+        elif [[ $RET -eq 0 ]]; then
+            echo Archiving Complete
             break;
         fi
     done