update_payload: Make paycheck take "root" instead of "rootfs"

This commit makes paycheck take "root" as the rootfs partition label
instead of "rootfs", which makes it consistent with other tooling like
delta_generator.

BUG=chromium:794404
TEST=test_paycheck.sh and run_unittests

Change-Id: I20835e93adbcde459bc86d832e695b38bca55e38
Reviewed-on: https://chromium-review.googlesource.com/1132843
Commit-Ready: Tudor Brindus <tbrindus@chromium.org>
Tested-by: Tudor Brindus <tbrindus@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
diff --git a/scripts/update_payload/applier.py b/scripts/update_payload/applier.py
index 49db8ae..c63e156 100644
--- a/scripts/update_payload/applier.py
+++ b/scripts/update_payload/applier.py
@@ -643,13 +643,13 @@
 
     manifest = self.payload.manifest
     if self.payload.header.version == 1:
-      for name in common.CROS_PARTITIONS:
-        new_part_info[name] = getattr(manifest, 'new_%s_info' % name)
-        old_part_info[name] = getattr(manifest, 'old_%s_info' % name)
+      for real_name, proto_name in common.CROS_PARTITIONS:
+        new_part_info[real_name] = getattr(manifest, 'new_%s_info' % proto_name)
+        old_part_info[real_name] = getattr(manifest, 'old_%s_info' % proto_name)
 
-        install_operations.append((common.ROOTFS, manifest.install_operations))
-        install_operations.append((common.KERNEL,
-                                   manifest.kernel_install_operations))
+      install_operations.append((common.ROOTFS, manifest.install_operations))
+      install_operations.append((common.KERNEL,
+                                 manifest.kernel_install_operations))
     else:
       for part in manifest.partitions:
         name = part.partition_name