Telnet: 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>
Could you check the messages are written to log here with:
Check Log Message   ${tc.kws[..].msgs[..]}    message    LEVEL