Check if the dest_file already exists on the file system (return boolean).

def check_file_exists(self, remote_cmd=""):
        """Check if the dest_file already exists on the file system (return boolean)."""
        if self.direction == "put":
            if not remote_cmd:
                remote_cmd = "dir {}{}".format(self.file_system, self.dest_file)
            remote_out = self.ssh_ctl_chan.send_command_expect(remote_cmd)
            search_string = r"{}.*Usage for".format(self.dest_file)
            if "No such file or directory" in remote_out:
                return False
            elif re.search(search_string, remote_out, flags=re.DOTALL):
                return True
            else:
                raise ValueError("Unexpected output from check_file_exists")
        elif self.direction == "get":
            return os.path.exists(self.dest_file)