XD-1614 Fix UTC endTime display

- The `endTime` attribute on job/step execution can be null if the job/step
execution is not yet complete by the time the test does the assertion
- Add `null` check on endTime in Job job/step execution display commands
- Fix test
XD-1620 Fix JobCommandTests

- Avoid using `JobExecution.getRows().get(0)`
  - Instead, get the matching jobExecution for the given job name and return the jobExecutionId for that row
- The same fix isn't needed for StepExecution list because they are retrieved on a given `jobExecutionId`