Move UpdateStatus and helpers to dedicated files

This allows us to easily share it between the update_engine proper
and a forthcoming client library.

Bug: 24547247
Test: mmm system/update_engine; emerge-panther update_engine

Change-Id: I8c0db7a0f95dd6368bfc886f1b0d1a9d2efb461f
diff --git a/update_engine.gyp b/update_engine.gyp
index 2a1768e..ec32550 100644
--- a/update_engine.gyp
+++ b/update_engine.gyp
@@ -51,6 +51,7 @@
       # We need this include dir because we include all the local code as
       # "update_engine/...".
       '<(platform2_root)/../aosp/system',
+      '<(platform2_root)/../aosp/system/update_engine/client_library/include',
     ],
   },
   'targets': [
@@ -213,6 +214,7 @@
         'update_manager/real_updater_provider.cc',
         'update_manager/state_factory.cc',
         'update_manager/update_manager.cc',
+        'update_status_utils.cc',
         'utils.cc',
         'xz_extent_writer.cc',
       ],