MFH: r503955
Fix named when using plugins and chroot.
BIND9 introduced plugins and migrated the filter-aaaa feature to a
plugin.
As it loads its plugins late in the startup process (read after chroot),
the plugins need to be available in the chroot.
Also, refactor the code now that a second directory need to be handled.
PR: 238011
Reported by: ryan@timewasted.me