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_generator/payload_file.cc b/payload_generator/payload_file.cc
index 941b640..a9e32a3 100644
--- a/payload_generator/payload_file.cc
+++ b/payload_generator/payload_file.cc
@@ -81,8 +81,8 @@
                                const vector<AnnotatedOperation>& aops) {
   // Check partitions order for Chrome OS
   if (major_version_ == kChromeOSMajorPayloadVersion) {
-    const vector<const char*> part_order = { kLegacyPartitionNameRoot,
-                                             kLegacyPartitionNameKernel };
+    const vector<const char*> part_order = { kPartitionNameRoot,
+                                             kPartitionNameKernel };
     TEST_AND_RETURN_FALSE(part_vec_.size() < part_order.size());
     TEST_AND_RETURN_FALSE(new_conf.name == part_order[part_vec_.size()]);
   }
@@ -152,7 +152,7 @@
         *(partition->mutable_new_partition_info()) = part.new_info;
     } else {
       // major_version_ == kChromeOSMajorPayloadVersion
-      if (part.name == kLegacyPartitionNameKernel) {
+      if (part.name == kPartitionNameKernel) {
         for (const AnnotatedOperation& aop : part.aops)
           *manifest_.add_kernel_install_operations() = aop.op;
         if (part.old_info.has_size() || part.old_info.has_hash())