Implement BDI plan step failure

[dhixsingh]

What is required is the ability to allow plan steps to fail. BDI plans are currently described by a sequence of plan steps as below:

jill/jill/src/test/java/io/github/agentsoz/jill/testprogram/PlanA.java

Lines 43 to 55 in 68aca1b

	PlanStep[] steps = {new PlanStep() {
	public void step() {
	((TestAgent) getAgent()).setStatus(((TestAgent) getAgent()).getStatus() | 0x0001);
	}
	}, new PlanStep() {
	public void step() {
	post(new GoalB("gB"));
	}
	}, new PlanStep() {
	public void step() {
	post(new GoalC("gC"));
	}
	},};

The solution is to update the following step() function to instead return a boolean to indicate if the step (which could be an atomic action in the environment, or a sub-goal) has failed:

jill/jill/src/main/java/io/github/agentsoz/jill/lang/PlanStep.java

Line 33 in c481e8c

public void step();

Then the intention selction machinery should to be updated to handle cases where a plan step returns false. If it does, then the plan must be aborted ie no further steps should be executed, and the plan itself should be failed (no mechanism to indicate plan failure exists yet either). The relevant code for this is here:

jill/jill/src/main/java/io/github/agentsoz/jill/core/IntentionSelector.java

Lines 254 to 258 in c481e8c

	} else {
	logger.debug(Log.logPrefix(agentIndex) + " is executing a step of plan "
	+ node.getClass().getSimpleName());
	node.step();
	}