Check key-directory duplicates for kasp zones

Check key-directory duplicates for kasp zones

Don't allow the same zone with different dnssec-policies in separate
views have the same key-directory.

Track zones plus key-directory in a symtab and if there is a match,
check the offending zone's dnssec-policy name. If the name is "none"
(there is no kasp for the offending zone), or if the name is the same
(the zone shares keys), it is fine, otherwise it is an error (zones
in views using different policies cannot share the same key-directory).