Fix the concat of strings for tests results.

The old test results would go over multiple lines (LFCR etc). Will
look at the other commands to see if they're also affected.
Re-work the retry timer to be single-shot.

The time will fire when each retry fails rather than at every
(interval)ms from the point that it originally failed.

This should mean that retries fire at the interval time of the response
coming back (which may work) rather than possibly firing early.
Concat strings for errors into string tcp write.
Cat of strings in the List command.