try to pull connection details from the munin-environment

if possible use the munin-node configuration via it's env to determine
which hostname and port to use. If there are no environment variables
fall back to localhost:4223
Make connection timeout configurable

Especially with long-distance stacks with RS485 or WiFi connected bricks
it is hard to get the value within the default time.

This makes this configurable via the munin-environment, failing back to
the builtin timeout from tinkerforge.ip_connection
Merge pull request #4 from klaernie/fix-host-config

Fix host configuration and add timeout via munin environment