Limit memory allocation of get_bytes to 1MB
If get_bytes() can pad unlimited, a RSA pub key could be crafted
that would allocate GB's of nulls, thereby forming a DoS-vector. https://github.com/paramiko/paramiko/commit/3bbcf808d8da43a379cee5ce3d004d3c6eb6e1b7
Fix SSHException when re-keying over a fast connection.  https://github.com/paramiko/paramiko/commit/c51b3b208c228fe6482ef00b3572a19683e7bb98