utils.pm: use FindBin instead of awk to find the path to
'use lib utils.pm' is not valid Perl syntax:
Bareword "utils" not allowed while "strict subs" in use at plugins-scripts/check_ircd.pl line 52.
Bareword "pm" not allowed while "strict subs" in use at plugins-scripts/check_ircd.pl line 52.
This makes it impossible to use the plugins directly from the git tree,
e.g. while hacking on them.
Using FindBin::Bin as the library path allows that, while preserving
the original behaviour of adding the libexec path when the plugin is
properly installed.