Fail job early when there is no input

Right now we get a cryptic error message when we know that there is no input!

2012-09-28 13:45:20,410 INFO org.apache.giraph.graph.BspServiceMaster: generateInputSplits: Got 0 input splits for 100 workers
2012-09-28 13:45:20,410 WARN org.apache.giraph.graph.BspServiceMaster: createInputSplits: Number of inputSplits=0 < 100=number of healthy processes, some workers will be not used

But the job keeps on going and the workers get the exception

java.lang.IllegalStateException: setup: loadVertices failed due to KeeperException
at org.apache.giraph.graph.BspServiceWorker.setup(BspServiceWorker.java:628)
at org.apache.giraph.graph.GraphMapper.setup(GraphMapper.java:370)
at org.apache.giraph.graph.GraphMapper.run(GraphMapper.java:570)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:632)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:307)
at org.apache.hadoop.mapred.Child.main(Child.java:171)
Caused by: org.apache.zookeeper.KeeperException$NoNodeException: KeeperErrorCode = NoNode for /_hadoopBsp/job_201209271814.325_0001/_inputSplitDir
at org.apache.zookeeper.KeeperException.create(KeeperException.java:102)
at org.apache.zookeeper.KeeperException.create(KeeperException.java:42)
at org.apache.zookeeper.ZooKeeper.getChildren(ZooKeeper.java:1243)
at org.apache.zookeeper.ZooKeeper.getChildren(ZooKeeper.java:1271)
at org.apache.giraph.zk.ZooKeeperExt.getChildrenExt(ZooKeeperExt.java:273)
at org.apache.giraph.graph.BspServiceWorker.reserveInputSplit(BspServiceWorker.java:225)
at org.apache.giraph.graph.BspServiceWorker.loadVertices(BspServiceWorker.java:320)
at org.apache.giraph.graph.BspServiceWorker.setup(BspServiceWorker.java:607)
... 5 more