CI: Confluence page: Fix not created mx6 section

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.