Make compatible with Python 2 and 3

Use Python 3 style print statements. Add `from __future__ import print_function`
for compatibility with Python 2.

Drop iniparse. It is a module which must be separately installed, it has not
received any updates since 2010, and the configparser module from the standard
library accomplishes the same end goal.

Drop the weird exception handling in the import section of
`katello_rapidnode.py`. It is redundant, as Python will throw an exception if a
module cannot be imported. It is also harder to read than normal imports, the
resultant errors provide less information than the standard error messages do
annoying to read, and it generally bothers me.

Both the Python 2 and Python 3 versions of flake8 and pylint now process
`katello_rapidnode.py` without producing any fatal errors.
`from __future__ import print_statement` allows this to be be 100% backward compatible with Python 2 linters.