Pipe http server log to hclog, so that it uses the same logging format
as rest of nomad logs. Also, supports emitting them as json logs, when
json formatting is set.
The http server logs are emitted as Trace level, as they are typically
repsent HTTP client errors (e.g. failed tls handshakes, invalid headers,
etc).
Though, Panic logs represent server errors and are relayed as Error
level.
