Refactor: cts,python: Move start_environment to the Test class.

This code is very similar between cts-exec and cts-fencing. The biggest
difference was in the list of daemons to start/stop, which can just be
class-specific methods.

Some log messages and command strings were nearly identical, which I
improved upon even though they are still in their own classes, just in
case we want to do more there in the future.

Also, only cts-fencing was cleaning up the log file between runs. Now
both classes will do so.