Allow odd worker count

[kboom]

For now odd worker counts cause the problem with partitioning

Exception in thread "org.apache.giraph.master.MasterThread" java.lang.IllegalStateException: java.lang.ArithmeticException: mode was UNNECESSARY, but rounding was necessary
	at org.apache.giraph.master.MasterThread.run(MasterThread.java:201)
Caused by: java.lang.ArithmeticException: mode was UNNECESSARY, but rounding was necessary
	at com.google.common.math.MathPreconditions.checkRoundingUnnecessary(MathPreconditions.java:81)
	at com.google.common.math.IntMath.log2(IntMath.java:91)
	at edu.agh.iga.adi.giraph.direction.PartitioningStrategy.partitioningStrategy(PartitioningStrategy.java:40)
	at edu.agh.iga.adi.giraph.direction.io.IgaTreeSplitter.allSplitsFor(IgaTreeSplitter.java:25)
	at edu.agh.iga.adi.giraph.direction.io.InMemoryStepInputFormat.getSplits(InMemoryStepInputFormat.java:77)
	at org.apache.giraph.io.internal.WrappedVertexInputFormat.getSplits(WrappedVertexInputFormat.java:72)
	at org.apache.giraph.master.BspServiceMaster.generateInputSplits(BspServiceMaster.java:329)
	at org.apache.giraph.master.BspServiceMaster.createInputSplits(BspServiceMaster.java:624)
	at org.apache.giraph.master.BspServiceMaster.createVertexInputSplits(BspServiceMaster.java:668)
	at org.apache.giraph.master.MasterThread.run(MasterThread.java:113)