Xpra: Ticket #2307: paramiko does not support the new openssh key format

It reports:

$ python -c "from paramiko import RSAKey;RSAKey.from_private_key_file('./test.rsa')"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python2.7/site-packages/paramiko/pkey.py", line 206, in from_private_key_file
    key = cls(filename=filename, password=password)
  File "/usr/lib/python2.7/site-packages/paramiko/rsakey.py", line 55, in __init__
    self._from_private_key_file(filename, password)
  File "/usr/lib/python2.7/site-packages/paramiko/rsakey.py", line 175, in _from_private_key_file
    data = self._read_private_key_file("RSA", filename, password)
  File "/usr/lib/python2.7/site-packages/paramiko/pkey.py", line 279, in _read_private_key_file
    data = self._read_private_key(tag, f, password)
  File "/usr/lib/python2.7/site-packages/paramiko/pkey.py", line 289, in _read_private_key
    raise SSHException("not a valid " + tag + " private key file")
paramiko.ssh_exception.SSHException: not a valid RSA private key file

With a key file generated using a recent ssh-keygen, the file looks like this:

-----BEGIN OPENSSH PRIVATE KEY-----
(key data)
-----END OPENSSH PRIVATE KEY-----

Instead of the older pem format:

-----BEGIN RSA PRIVATE KEY-----
Proc-Type: 4,ENCRYPTED
DEK-Info: DES-EDE3-CBC,48F3BB90CF126AB9
(key data)
-----END RSA PRIVATE KEY-----

And so the connection fails with the message: not a valid RSA private key file. r22779 improves things and will continue and try other keyfiles, password auth, etc but this doesn't help loading this new key format.