Krb5Admin::Log: strip curve25519_* public keys from the log.
change mode of file...
Change krb5_hostd to work a little more like krb5_admind.

We break the functionality out into Krb5Admin::Krb5Host::Daemon to make
krb5_hostd a little simpler.  We also add Krb5Admin::Krb5Host::Log to
strip the logs a little before writing them---we remove the public keys
and nonces from the CURVE25519_NWAY calls...