delta_generator: Use "kernel" and "root" partition names internally

This commit abandons using "boot" and "system" names internally for
major version 1 payloads in favor of "kernel" and "root", which is
symmetrical with what's used in major version 2 payloads.

BUG=chromium:794404
TEST=no errors running brillo_update_payload with FORCE_MAJOR_VERSION
  set to either 1 or 2; paycheck.py <generated payload> --check and
  printing partition names in protobuf confirms correct names are
  generated

Change-Id: I396274812d5586e19a021c05b8b7a415aac976bf
Reviewed-on: https://chromium-review.googlesource.com/1119573
Commit-Ready: Tudor Brindus <tbrindus@chromium.org>
Tested-by: Tudor Brindus <tbrindus@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
diff --git a/payload_consumer/delta_performer.cc b/payload_consumer/delta_performer.cc
index a986b07..86bd6c3 100644
--- a/payload_consumer/delta_performer.cc
+++ b/payload_consumer/delta_performer.cc
@@ -800,7 +800,7 @@
   } else if (major_payload_version_ == kChromeOSMajorPayloadVersion) {
     LOG(INFO) << "Converting update information from old format.";
     PartitionUpdate root_part;
-    root_part.set_partition_name(kLegacyPartitionNameRoot);
+    root_part.set_partition_name(kPartitionNameRoot);
 #ifdef __ANDROID__
     LOG(WARNING) << "Legacy payload major version provided to an Android "
                     "build. Assuming no post-install. Please use major version "
@@ -822,7 +822,7 @@
     partitions_.push_back(std::move(root_part));
 
     PartitionUpdate kern_part;
-    kern_part.set_partition_name(kLegacyPartitionNameKernel);
+    kern_part.set_partition_name(kPartitionNameKernel);
     kern_part.set_run_postinstall(false);
     if (manifest_.has_old_kernel_info()) {
       *kern_part.mutable_old_partition_info() = manifest_.old_kernel_info();