1. cu -l /dev/nmdm0001A
2. In another window, verify that there are /dev/nmdm0001A and
/dev/nmdm0001B devices
3. Start a 'cu -l /dev/nmdm0001B' and verify bidirectional flow of
typed chars between the two cu sessions
4. Exit the first cu session and restart it, and verify that the
system doensn't crash, and that data flows as per step 3.
5. Repeat the above steps with various device names.