When parsing remote messages, require them to have standard timestamp
field, and support properly parse out the hostname as described by RFC3164,
which wasn't done before. However, don't discard message if it doesn't
have hostname, for compatibility.

Enable logging of the message supplied hostname instead of real hostname
with -H switch.

PR: 200933
Reported by: Konstantin Pavlov <thresh nginx.com>
MFC after: 2 months