allow for ssh-specific arguments

Hi,

scp and scp are not necessarily argument compatible. For example, the -R switch (which allows you to create a reverse tunnel) is usable on SSH only and not SCP. I am trying to use this in an ansible script but unfortunately there is no configuration option to pass arguments to just the ssh command and not scp/sftp.

This code allows you to specify commands that will only be passed to ssh via ssh_specific_args in ansible.cfg.