* Fix filedescriptor out of range in select() when running commands
* Simplify the run_command() code
Now that we're using selectors in run_command(), we can simplify some of
the code.
* Use fileobj.read() instead of os.read()
* No longer use get_buffer_size() as we can just slurp all of the data
instead.
Also use a simpler conditional check of whether the selector map is
empty
Co-authored-by: Toshio Kuratomi <a.badger@gmail.com>
