Base class for CLI returns a dictionary.

The 'execute' method now returns a python dictionary containing the
results for stdout, stderr and return code of the command executed. It
is up to the test implementer how to properly handle the results
returned.

I have also applied some PEP8 love and fixed some tests that were
broken.

TODO: test_Host.py needs to be updated so that all required values are
generated from existing methods.
Merge pull request #148 from omaciel/refactor_error_code

Base class for CLI returns a dictionary.