terminal.py: Fix Xfce on ubuntu/debian; some cleanup
* Xfce class was setting and passing wrong variable for ubuntu/debian.
* Xfce class was using -e instead of -x for passing command. The former creates
a shell escape nightmare
* Clean up local and instance/class variables with same name but different usage.
* Remove side-effect and directly return formatted command for clarity.
Signed-off-by: Jeffrey C Honig <jeffrey.honig@windriver.com> Signed-off-by: Saul Wold <sgw@linux.intel.com>
