Allow the VT tests to run on OSX

@rallytime please double check and merge this if working as supposed.
Unfortunately, this isn't working either. The `proc` object is getting created, but it doesn't contain anything in `stdout`.  If I break down the command and do a `sysctl -a | grep pty.nr`, no results are returned. Nothing is found with either `sysctl -a | grep pty` or `sysctl -a | grep nr` that is related. The only thing I can find about this is getting the max number of pseudo-terminals with: `sysctl -a | grep tty` which gives: `kern.tty.ptmx_max: 127`