Use openssh for interactive 'lago shell' instead of paramiko

[didib]

IMO we should use /usr/bin/ssh - OpenSSH - at least for interactive shells - instead of paramiko, at least for these two reasons:

• openssh has some escape sequences for controlling it (search its man page for 'escape'). In particular, <~><.> disconnects the session, which is more convenient than having to search for the stuck lago process and killing it from another shell.

• At least once, it failed for me due to the internal shell (inside the host) outputting an invalid UTF-8 sequence, with [1]. This in itself is probably easy to fix by catching the exception.

• Pressing 'PageUp'/PageDown' keys inside 'less' does not work. Workaround: export TERM=(your real term) (in my case, 'screen', which is what tmux sets).

[1]

[ *** ] (2 oError occured, aborting
Traceback (most recent call last):
File "/usr/lib/python3.6/site-packages/lago/ssh.py", line 279, in
drain_ssh_channel
stdout.write(out)
TypeError: write() argument must be str, not bytes

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/usr/lib/python3.6/site-packages/lago/cmd.py", line 987, in main
cli_plugins[args.verb].do_run(args)
File "/usr/lib/python3.6/site-packages/lago/plugins/cli.py", line
186, in do_run
self._do_run(**vars(args))
File "/usr/lib/python3.6/site-packages/lago/utils.py", line 584, in wrapper
return func(*args, **kwargs)
File "/usr/lib/python3.6/site-packages/lago/utils.py", line 595, in wrapper
return func(*args, prefix=prefix, **kwargs)
File "/usr/lib/python3.6/site-packages/lago/cmd.py", line 480, in do_shell
result = host.interactive_ssh(['bash'])
File "/usr/lib/python3.6/site-packages/lago/plugins/vm.py", line
106, in wrapper
return func(self, *args, **kwargs)
File "/usr/lib/python3.6/site-packages/lago/plugins/vm.py", line
720, in interactive_ssh
password=self._spec.get('ssh-password'),
File "/usr/lib/python3.6/site-packages/lago/ssh.py", line 205, in
interactive_ssh
return interactive_ssh_channel(channel, ' '.join(command))
File "/usr/lib/python3.6/site-packages/lago/ssh.py", line 314, in
interactive_ssh_channel
return utils.CommandStatus(*drain_ssh_channel(chan, stdin))
File "/usr/lib/python3.6/site-packages/lago/ssh.py", line 281, in
drain_ssh_channel
stdout.write(out.decode('utf-8'))
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xe2 in position
31: unexpected end of data