Enable config option in TelnetLibrary for python telnetlib

To be able to change the logging behavior of the underlying python
telnetlib a new parameter is added in the open connection keyword.

Signed-off-by: Heiko Thiery <heiko.thiery@kontron.com>
1) There's a typo in `loggin`, two spaces before `python`, and it should actually be `Python`.

2) The first line of the doc is the short doc of the keyword and it should not be cut. It could be something fairly generic and then more information can be in a paragraph below. For details see https://www.python.org/dev/peps/pep-0257/.

3) There should be a note that this keyword is new in Robot Framework 2.8.7.