Unable to check result "undefined" in cli

https://issues.jboss.org/browse/WFLY-4118
> The ModelNode getting compared will be of type 'Object', or 'List' maybe, because a singular value type (bool, string, int, etc) couldn't be located as the path didn't exist.

That's actually why it would be inconsistent for non-existing paths. resolveValue in ModelNodePathOperand should either return the ModelNode value which represents the last element in the path (meaning that the path is a valid one, i.e. exists) or null. It shouldn't return a ModelNode value for something in the middle.
Taking into account the current impl of ComparisonOperation.resolveValue(...) this will resolve to false for non-existing types even for NotEquals.

Then when we add support for path-exists check, instead of returning null for non-existing path in ModelNodePathOperand.resolveValue(...) we'd throw an error.

What do you think about this?