Returns a service parse error on overrides across the treble boundary.

Also includes new --out_<partition> flags for
  system,system_ext,product,vendor,odm
to allow host_init_verifier to work with a collection of init rc files.

Test: host_init_verifier --out_system=... --out_vendor=...
      where vendor contains an init rc file that overrides a service
      present in system. Observe parse failure and non-zero exit.
Bug: 163089173
Change-Id: I520fef613e0036df8a7d47a98d47405eaa969110
diff --git a/init/service.h b/init/service.h
index bc5c90f..aee1e5d 100644
--- a/init/service.h
+++ b/init/service.h
@@ -137,6 +137,7 @@
             flags_ &= ~SVC_ONESHOT;
         }
     }
+    Subcontext* subcontext() const { return subcontext_; }
 
   private:
     void NotifyStateChange(const std::string& new_state) const;
@@ -168,6 +169,7 @@
     std::vector<FileDescriptor> files_;
     std::vector<std::pair<std::string, std::string>> environment_vars_;
 
+    Subcontext* subcontext_;
     Action onrestart_;  // Commands to execute on restart.
 
     std::vector<std::string> writepid_files_;