ServerToGrpcAddress and GrpcAddressToServerAddress called glog.Fatalf
when hostAndPort could not parse the port, which os.Exit(255)ed the whole
process. A caller-supplied copy or tail source address reached this path
synchronously in the serving goroutine, so one anonymous VolumeCopy with
a non-numeric port terminated the volume server.
Log the parse error and return the input unchanged instead: the dial or
request that consumes the address then fails as an ordinary error.
Chris Lu
47f323bbb3