Fix telnet action plugin type error

[Nifi]

SUMMARY

Fixes #36199
The telnet module gave the following error:
TypeError: a bytes-like object is required, not 'AnsibleUnicode'
This commit fixes this error by changing the types of the str type arguments to telnetlib to bytes types.

ISSUE TYPE

• Bugfix Pull Request

COMPONENT NAME

telnet action plugin

ANSIBLE VERSION

ansible 2.7.0.dev0
  config file = None
  configured module search path = ['/home/nicolas/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python3.6/site-packages/ansible-2.7.0.dev0-py3.6.egg/ansible
  executable location = /usr/bin/ansible
  python version = 3.6.6 (default, Jun 27 2018, 13:11:40) [GCC 8.1.1 20180531]