How can I ensure that only one if a kind of Jenkins job is run?

Use the Throttle Concurrent Builds Plugin. It replaces the Locks and Latches plugin, and provides the capability to restrict the number of jobs running for specific labels.

For example: you create a project category 'Integration Test Server A' and tie jobs to it with a maximum concurrent count of 1, and a second 'Integration Test Server B' label and tie other jobs to it, both categories will only run a single concurrent build (assuming you've set a max job count of 1), and the other jobs in that category will queue until the 'lock' has cleared.

Using this method, you don't have to restrict the number of executors available on any specific Jenkins instance, and can easily add further slaves in the future without having to reconfigure all your jobs.