flow: supress error log message for simple health-checking (#36)
flow: supress error log message for simple health-checking (#36)

We don't want probing from load balancers or Prometheus to cause the
error log to be noisy. This revision is supressing the logging to the
error log in the following cases:

(1) 'message of type 127 and size 0 failed decoding at field 0: <nil>'

This can be trigger using "echo -e '\xff\xff\xff' | nc ...".

(2) 'error reading from unknown: EOF'

This can be trigger using nc to connect to a tcp Vanadium endpoint
and then typing Ctrl-C after receiving the first message. Another way
is using 'nc ... & p=$! && sleep 1 && kill -s SIGINT ${p}'

(3) 'read: connection reset by peer'.

This can be trigger using 'nmap -sT' to a tcp Vanadium endpoint.
vanadium/core,vanadium/core,vanadium/core,vanadium/core