Split execution of interactive command to its own methods.
Split execution of interactive command to its own methods.

The execution of interactive commands is now defined in the
'interactive' method (for both 'Local' and 'Remote' objects) instead of
using the special 'INTERACTIVE' option of the 'execute' method.

Two context managers '_get_chan' and '_forward_agent' have also be
defined for:
    * closing the agent forwarder and the channel after the execution of
      a command,
    * having reusable and more readable code between methods that
      execute commands

fmenabe/python-unix