Fixes contributing to JSR decider tests

Prevent NPE when checking for a re-runnable continued flow, remove usage of state transition comparator in FlowParser, ensure custom exit code is set at job level.

Fixes TCK test testDeciderExitStatusIsSetOnJobContext, contributes but does not fix decider transition tests that include restart.

NOTE: for the time being I am excluding testDeciderTransitionFromStepWithinFlowAndAllowRestartFalse from my TCK tests as it results in an infinite loop