healthd: Fixups for systems without batteries or removable batteries

* Replace unnecessary warnings about missing attributes with a more
  informative message when no battery devices provided by the system.

* Turn off periodic battery checks when no battery devices (thereby
  reducing unnecessary kernel log spam).

* Replace battery properties in log messages with a more informative
  message when no battery is provided or the battery is removed.

Change-Id: I68a514aa7315ae2b5d22cb8861d3c9b1b38035a1
diff --git a/healthd/BatteryMonitor.h b/healthd/BatteryMonitor.h
index 3dd2ef0..f0e6454 100644
--- a/healthd/BatteryMonitor.h
+++ b/healthd/BatteryMonitor.h
@@ -44,6 +44,7 @@
   private:
     struct healthd_config *mHealthdConfig;
     Vector<String8> mChargerNames;
+    bool mBatteryDevicePresent;
 
     int getBatteryStatus(const char* status);
     int getBatteryHealth(const char* status);