public JobDefinition getJobDefinition(String jobName) {
		for (JobDefinition jd : getJobDefinitions()) {
			if (jd.getJobName().equals(jobName)) {
				return jd;
			}
		}
		return null;
	}
Construct a transition link, and possibly a new node if a suitable candidate does not already exist.
If a transition has already referenced a particular job in the same flow, reuse it. If not then
create a new node and link to it.

@param fromJobNodeId the id of the jobnode from which the transition is occurring
@param jobExitStatus the job exit status attached to this transition
@param targetJobName the transition target
@return the ID of the transition target node if a new node created, otherwise -1
spring-xd-dirt/src/main/java/org/springframework/xd/dirt/job/dsl/JobSpecification.java