certctl: fix hashed link generation with duplicate subjects

Currently, certctl rehash will just keep clobbering .0 rather than
incrementing the suffix upon encountering a duplicate. Do this, and do it
for blacklisted certs as well.

This also improves the situation with the blacklist to be a little less
flakey, comparing cert fingerprints for all certs with a matching subject
hash in the blacklist to determine if the cert we're looking at can be
installed.

Future work needs to completely revamp the blacklist to align more with how
it's described in PR 246614. In particular, /etc/ssl/blacklisted should go
away to avoid potential confusion -- OpenSSL will not read it, it's
basically certctl internal.

PR: 246614
Reviewed by: Michael Osipov <michael.osipov siemens com>
Tested by: Michael Osipov
With suggestions from: Michael Osipov
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D26167