Sanitize snowflake.log

For starters, the timestamps are in the local timezone. We can make that UTC

Known problems:

The client logs full SDP stanzas, which include local IP addresses.
When the websocket server panics (as in #29125 (moved)), it writes the client IP address to the log: {{{ 2019/01/18 18:56:29 http2: panic serving X.X.X.X:YYYY: interface conversion: *http2.responseWriter is not http.Hijacker: missing method Hijack }}}
The websocket server logs an IP address on certain connection errors. (These are probably automated scanners, but still...) {{{ 2019/04/01 07:02:50 http: TLS handshake error from X.X.X.X:YYYY: acme/autocert: missing server name 2019/04/01 07:53:03 http: TLS handshake error from X.X.X.X:YYYY: tls: oversized record received with length 21536 }}}
The broker logs the raw bytes of ICE answers: {{{ 2019/03/22 06:28:32 Received answer: [XXX XXX XXX XXX ... XXX] }}}

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