net-analyzer/nagios-core: synchronize econf and web server paths.

net-analyzer/nagios-core: synchronize econf and web server paths.

The nagios ./configure script takes two custom "cgibindir" and
"webdir" paths that tell it where to put its CGI files and public
document root. The web server configuration files that we ship also
need to know these paths, which normally wouldn't be a problem, except
that they involve a call to $(get_libdir).

There doesn't seem to be an elegant place to upstream these conf files
(which are Gentoo-specific), so we adopt the next-best solution: use
@CGIBINDIR@ and @WEBDIR@ as placeholders, and then replace them with
sed in src_configure().

For consistency with the PMS definition of econf, these paths (and all
others) now have EPREFIX prepended.

Closes: https://bugs.gentoo.org/699002
Package-Manager: Portage-2.3.76, Repoman-2.3.16
Signed-off-by: Michael Orlitzky <mjo@gentoo.org>