Unable to check result "undefined" in cli

https://issues.jboss.org/browse/WFLY-4118
This gets complicated because the problems, path-exists and not-equals, overlap slightly.

If we try to do not-equals first, the path-exists problem will cause a '!=' operation to return true instead of false. 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 won't equal whatever the comparison type is in the if-else statement, and 'true' will result. All other operations comparing non-existent paths will still return 'false' though. Creating inconsistent behavior when comparing non-existent paths.

If we want non-existent paths to continue always returning false we have to fix that problem before fixing the not-equals problem.

The existing PR, as it stands, adds 'undefined' comparison functionality to the existing, though bugged, framework. I think we have to either merge this PR and work on the path-exists and not-equals problems separately, or add another commit here that fixes them both.

I'd prefer fixing them it all here, but it depends on how you want to track it.