Fix the behaviour for atomic top where if you want to include
additional fields to monitor, you now specificy one field per
-o switch. For example:
atomic top -o ppid -o time
Closes: #780
Approved by: baude
Basic tests for atomic diff and top which should catch
basic code regressions.
In top.py, added -n for number of iterations. And added
tty detection so that tests can pass in a jenkins environment
where there is no tty.
