S3 Connection Logging: Copy-Paste errors

[ifadams]

Describe the bug
Very minor bug, but noting that the errors the get logged to STDERR are occasionally copy-paste and slightly misleading, e.g. a connection error for a read reporting as WRITE error redirected to cerr.

For example, in RemoteConnection.cc, this is a read/retrieval operation, but we are logging a WRITE error to STDERR.

void RemoteConnection::RetrieveFile(const std::string &filename) {
  if (_remote_connected) {
    retrieve_file(filename);
  } else {
    std::cerr << "WRITE: The RemoteConnection has not been started"
              << std::endl;
  }

Expected behavior

Error prefixes should reflect the approximate source of the error location.