node: munin plugin config ignores leading *

According to the docs here:
https://munin.readthedocs.org/en/latest/plugin/use.html#configuring

[<plugin-name>]
    The following lines are for <plugin-name>. May include one
wildcard (‘*’) at the start or end of the plugin-name, but not both,
and not in the middle.

However, this wasn't the case since the config parser only handled the
case where the wildcard is at the end.
ChangeLog: 2.0.22