[yocto] [ptest-runner][PATCH v2] 3 old patches + utils: ensure child can be session leader

[Randy MacLeod]

My patch needs Richards previous 3 patches so I've added them here.

I've cleaned up the patch a bit since v1; mostly it's indentation and
other cosmetic changes. I have added a bit more error handling and
I've renamed get_slave_pty to setup_slave_pty to more accurately 
reflect what the function does. Also I've cleaned up the code to only
use open_pty() to get the tty name.

Care to release an update now that oe-core 2.8-M1 is in QA?

../Randy