Clarify why we're logging a specific failure.

#2134 (comment)
-------------
Created by MOE: https://code.google.com/p/moe-java
MOE_MIGRATED_REVID=101240012

guava/src/com/google/common/util/concurrent/AggregateFuture.java

@@ -184,7 +184,11 @@ private void handleException(Throwable throwable) {
  // | and & used because it's faster than the branch required for || and &&
  if (throwable instanceof Error
  | (allMustSucceed & !completedWithFailure & firstTimeSeeingThisException)) {
- logger.log(Level.SEVERE, "input future failed.", throwable);
+ String message =
+ (throwable instanceof Error)
+ ? "Input Future failed with Error"
+ : "Got more than one input Future failure. Logging failures after the first";
+ logger.log(Level.SEVERE, message, throwable);
  }
  }