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/payload_generator/payload_file.h b/payload_generator/payload_file.h
index 6e0776c..7cf9160 100644
--- a/payload_generator/payload_file.h
+++ b/payload_generator/payload_file.h
@@ -17,9 +17,9 @@
 #ifndef UPDATE_ENGINE_PAYLOAD_GENERATOR_PAYLOAD_FILE_H_
 #define UPDATE_ENGINE_PAYLOAD_GENERATOR_PAYLOAD_FILE_H_
 
-#include <map>
 #include <string>
 #include <vector>
+#include <utility>
 
 #include <chromeos/secure_blob.h>
 #include <gtest/gtest_prod.h>  // for FRIEND_TEST
@@ -41,7 +41,7 @@
 
   // Sets the list of operations to the payload manifest. The operations
   // reference a blob stored in the file provided to WritePayload().
-  void AddPartitionOperations(PartitionName name,
+  bool AddPartitionOperations(const std::string& partition_name,
                               const std::vector<AnnotatedOperation>& aops);
 
   // Write the payload to the |payload_file| file. The operations reference
@@ -77,16 +77,13 @@
   // Print in stderr the Payload usage report.
   void ReportPayloadUsage(uint64_t metadata_size) const;
 
-  // The list of partitions in the order their blobs should appear in the
-  // payload file.
-  static const std::vector<PartitionName> partition_disk_order_;
-
   // The major_version of the requested payload.
   uint64_t major_version_;
 
   DeltaArchiveManifest manifest_;
 
-  std::map<PartitionName, std::vector<AnnotatedOperation>> aops_map_;
+  std::vector<std::pair<std::string,
+                        std::vector<AnnotatedOperation>>> aops_vec_;
 };
 
 // Adds a dummy operation that points to a signature blob located at the