use_node_name breaks datafile import

[azrdev]

running muninflux import doesn't succeed processing /var/lib/munin/datafile. The offending line reads like example.com;host:use_node_name 0 - opposed to the other, plugin-related lines, there is only one string after the host specification, instead of multiple .-separated ones.

[chrimi]

this happens too on the following lines:
domain;host:port 4949
domain;host:update 1

fixed it meanwhile locally doing a check on the plugin_parts length (will add a PR as soon as possible here)