YADE should substitute variables in the ssh_auth_file parameter if used from included fragments

Current Situation

• YADE does not substitute variables in the ssh_auth_file parameter if used from included fragments.
• Configuration sample:

  [protocol_fragment_sftp@sftp_server_2_local_key]
  protocol                            = sftp
  
  host                                = test.sos-berlin.com
  port                                = 22
  user                                = demo
  ssh_auth_method                     = publickey
  
  ; this works NOT
  ssh_auth_file                       = ${USERPROFILE}\jade_demo\demo_id_rsa
  
  ; this works
  ;ssh_auth_file                       = c:\users\ap\jade_demo\demo_id_rsa
  
  [profile@sftp_server_2_local_key]
  operation                           = copy
  
  source_include                      = protocol_fragment_sftp@sftp_server_2_local_key
  file_spec                           = ^test\.txt$
  source_dir                          = /
  
  target_protocol                     = local
  target_host                         = localhost
  target_dir                          = ${USERPROFILE}\jade_demo\a
  
  ; this works
  ;source_ssh_auth_file                = ${USERPROFILE}\jade_demo\demo_id_rsa
  

• Use of this example results e.g. in a private key file name 'C:\tmp\${USERPROFILE}\jade_demo\demo_id_rsa' instead of 'C:\users\ap\jade_demo\demo_id_rsa'. Subsequently authentication fails with the source server and the transfer ends with error.

Desired Behavior

• Substitution of variables in the ssh_auth_file parameter should work for included fragments.
• This behavior should be checked for other parameters that might be affected as well.