Don't reflect unescaped cert data to the logs

Don't reflect unescaped cert data to the logs

Commit 3a0e385048 introduced a new path for unauthenticated bytes from
the client certificate to be printed unescaped to the logs. There are a
handful of these already, but it doesn't make sense to keep making the
problem worse. \x-escape any unprintable bytes.

The test case introduces a revoked UTF-8 certificate. This requires the
addition of the `-utf8` flag to `openssl req`. Since the existing
certificates all use an ASCII subset, this won't modify the existing
certificates' subjects if/when they get regenerated; this was verified
experimentally with

    $ make sslfiles-clean
    $ make sslfiles

Unfortunately the test can't be run in the CI yet due to a test timing
issue; see 55828a6b60.

Author: Jacob Champion <jchampion@timescale.com>
Discussion: https://www.postgresql.org/message-id/CAAWbhmgsvHrH9wLU2kYc3pOi1KSenHSLAHBbCVmmddW6-mc_=w@mail.gmail.com