ssh key discovery doesn't work with python-x2go

Bug reported migrated from https://bugs.x2go.org/cgi-bin/bugreport.cgi?bug=1348

If a profile enables "Discover SSH keys or use SSH agent for X2Go authentication" (that's from the PyHoca-GUI profile editor), then neither pyhaca-gui nor pyhoca-cli can connect. The result is "pyhoca-cli: error: No existing session". Explicitly specifying the SSH private key works. The x2goclient (non-python) does not have this problem.

Here is some debug output of the failure.

wjc@nyuknyuk:~$ pyhoca-cli --libdebug -P stormy
pyhoca-cli[3957] NOTICE: preparing requested X2Go session
pyhoca-cli[3957] (PyHocaCLI) NOTICE: preparing requested X2Go session
pyhoca-cli[3957] (x2goinifiles-pylib) INFO: proposed config files are ['
*/home/wjc/*.x2goclient/sessions']
pyhoca-cli[3957] (x2goinifiles-pylib) INFO: config files found: ['
*/home/wjc/*.x2goclient/sessions']
pyhoca-cli[3957] (x2goinifiles-pylib) INFO: proposed config files are ['
*/home/wjc/*.x2goclient/settings']
pyhoca-cli[3957] (x2goinifiles-pylib) INFO: config files found: ['
*/home/wjc/*.x2goclient/settings']
pyhoca-cli[3957] (x2goinifiles-pylib) INFO: proposed config files are ['
*/home/wjc/*.x2goclient/printing']
pyhoca-cli[3957] (x2goinifiles-pylib) INFO: config files found: ['
*/home/wjc/*.x2goclient/printing']
pyhoca-cli[3957] (x2gosession-pylib) DEBUG: X2Go control session parameters
for profile stormy:
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     username: wjc
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     key_filename:
*/home/wjc/*.ssh/id_rsa

pyhoca-cli[3957] (x2gosession-pylib) DEBUG: unique_hostkey_aliases: False
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     look_for_keys: True
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     allow_agent: True
pyhoca-cli[3957] (x2gosession-pylib) DEBUG: X2Go terminal session
parameters for profile stormy:
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     client_encoding: ISO8859-1
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     set_session_title: False
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     snd_system: pulse
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     xinerama: False
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     server_encoding: UTF-8
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     kbtype: auto
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     rdp_server:
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     snd_port: 4713
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     applications:
[u'WWWBROWSER', u'MAILCLIENT', u'OFFICE', u'TERMINAL']
pyhoca-cli[3957] (x2gosession-pylib) DEBUG: published_applications: False
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     cmd: XFCE
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     link: lan
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     xdmcp_server: localhost
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     kbvariant: null
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     geometry: 1440x900
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     rdp_options:
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     session_type: desktop
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     convert_encoding: False
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     clipboard: both
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     kblayout: us
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     session_title:
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     dpi: 96
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     pack: 16m-jpeg-9
pyhoca-cli[3957] (x2gosession-pylib) DEBUG: X2Go sshproxy parameters for
profile stormy:
pyhoca-cli[3957] (x2gosession-pylib) DEBUG: sshproxy_look_for_keys: False
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     sshproxy_host:
pyhoca-cli[3957] (x2gosession-pylib) DEBUG: sshproxy_key_filename:
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     sshproxy_user:
pyhoca-cli[3957] (x2gosession-pylib) DEBUG:     sshproxy_port: 22
pyhoca-cli[3957] (x2gosession-pylib) DEBUG: initializing X2GoControlSession
pyhoca-cli[3957] (x2gosessregistry-pylib) NOTICE: registering X2Go session
stormy...
pyhoca-cli[3957] (x2gosessregistry-pylib) DEBUG: registering X2Go session
with UUID 3902ce3c-f052-11e8-8b86-94c6911c02ca
pyhoca-cli[3957] (x2goclient-pylib) NOTICE: initializing X2Go session...
pyhoca-cli[3957] (x2gocontrolsession-pylib) NOTICE: connecting to [
stormy.carpenter.org]:22
pyhoca-cli[3957] (x2gocontrolsession-pylib) DEBUG: trying SSH key discovery
or agent authentication with server
No handlers could be found for logger "paramiko.transport"
pyhoca-cli: error: No existing session
pyhoca-cli[3957] (x2goguardian-pylib) DEBUG: X2Go session guardian thread
waking up after 1 seconds
pyhoca-cli[3957] (x2goguardian-pylib) DEBUG: calling session cleanup on
profile stormy for terminal session: