update_engine: More accurate and general method name

This is a small review that merely changes |UpdateAttempter|'s member
function |IsUpdateRunningOrScheduled()| to a more accurate name and
general name of |IsBusyOrUpdateScheduled()|.

BUG=none
TEST=FEATURES="test" emerge-$BOARD update_engine

Change-Id: I4dcce374c86f61e6cee9d060d915110765a70a79
diff --git a/update_attempter.h b/update_attempter.h
index 3b580ad..880e975 100644
--- a/update_attempter.h
+++ b/update_attempter.h
@@ -407,8 +407,8 @@
   // policy is available again.
   void UpdateRollbackHappened();
 
-  // Returns whether an update is currently running or scheduled.
-  bool IsUpdateRunningOrScheduled();
+  // Returns if an update is: running, applied and needs reboot, or scheduled.
+  bool IsBusyOrUpdateScheduled();
 
   void CalculateStagingParams(bool interactive);