The function that merges the variables of the different jobs, i.e:

`MACHINE="mx6"`

`MACHINE="mx6ull"`

used python `in` to check if a value already exists.
But `"mx6" in "mx6ull"` is true, so mx6 was dropped.
This rewrites it, storing the variables in a set (which is unique
automatically) instead of space seperated strings.
Space seperation is added before printing the variables to be used on
on the shell.