Get the file size of the remote file.

def remote_file_size(self, remote_cmd="", remote_file=None):
        """Get the file size of the remote file."""
        if remote_file is None:
            if self.direction == "put":
                remote_file = self.dest_file
            elif self.direction == "get":
                remote_file = self.source_file
        remote_cmd = 'system "ls -l {}/{}"'.format(self.file_system, remote_file)
        remote_out = self.ssh_ctl_chan.send_command(remote_cmd)
        for line in remote_out.splitlines():
            if remote_file in line:
                file_size = line.split()[4]
                break
        if "Error opening" in remote_out or "No such file or directory" in remote_out:
            raise IOError("Unable to find file on remote system")
        else:
            return int(file_size)