Make server connection read/write robust to partial message read/write

[jn9e9]

currently interfaces/operations/operations_client.go Client.operation() assumes that the whole of a request is successfully written to the output writer in one go, whereas the write api allows for only part of the buffer to be written in any one transaction.

On the read side, for the response, it also assumes that the whole of the response is received in one go. It also does not copy with resynchronisation to find a new header magic number if it finds itself in a confused state