Don't use -t -t for scp commands when tty enabled in salt-ssh
Discard stderr for salt-ssh with tty

Because we're using a tty, we only get a combined stdout and stderr. So
we throw away the stderr from our salt command and we don't worry about
the lack of an RSTR in the stderr on the master side
Merge pull request #19065 from basepi/salt-ssh-tty-16847

Fix salt-ssh with sudo and tty enabled