Backport the fixes from @yut23

[ELLIOTTCABLE]

This branch seems to have Python 3 support, amongst other things. Can you merge these changes upstream?

https://github.com/yut23/ssh-ident

[maddes-b]

That are quite a lot of changes in that fork. What changes are actually imporant functionalities?

ssh-ident was always working for Python 3, but defaulted to executable python (which is Python 2).
That was changed recently in f8bfac1

[maddes-b]

Using logging module was adapted with 0f253ec.

I do not see many bugs fixed:

• Fix direction of stdout for subprocesses

but several enhancements:

• using shlex module methods (not available in 2.7)
• support for the NERSC sshproxy.sh
• support for TMUX
• no ssh-agent if no identity matches