Guest execution doesn't properly send stdout/stderr with Linux guest and Mac host

[mitchellh]

This is easy to reproduce:

VBoxManage guestcontrol foo execute --timeout 5000 --username foo --password foo --wait-exit --wait-stdout --wait-stderr -- /bin/bash -c 'echo foo'

The result is no data is outputted on the host machine on STDOUT or STDERR, although an "echo foo" did take place.

If I remove the --wait-stderr then the stdout comes through fine.