Move install operations to partitions field in major version 2.

install_operations and kernel_install_operations will be empty in major
version 2, they are now present in partitions field.

partition_info are still in old location, more refactoring are needed before
moving them.

This patch also moves the kLegancyPartitionName constants from install_plan.h
to payload_constants.h.

TEST=cros_generate_update_payload generate same payload version 1 as before.
Call delta_generator manually with --major_version=2, then cros payload show.
cros_workon_make update_engine --test

Bug: 23694580
Change-Id: If9e9531656480b1174e13b39af7ecb6a81060aac
diff --git a/install_plan.cc b/install_plan.cc
index 382eb4e..ec2ee93 100644
--- a/install_plan.cc
+++ b/install_plan.cc
@@ -18,15 +18,13 @@
 
 #include <base/logging.h>
 
+#include "update_engine/payload_constants.h"
 #include "update_engine/utils.h"
 
 using std::string;
 
 namespace chromeos_update_engine {
 
-const char* kLegacyPartitionNameKernel = "boot";
-const char* kLegacyPartitionNameRoot = "system";
-
 InstallPlan::InstallPlan(bool is_resume,
                          bool is_full_update,
                          const string& url,