MDL-31832 CLI upgrade will return 0 exit status if no upgrade is needed
MDL-31832 CLI upgrade will return 0 exit status if no upgrade is needed

Discussed with David, both points were valid but finally
we agreed about to consider the "no upgrade needed" exit
a normal/succesful one, mainly because it keeps previous
behavior the same (exit non-zero only for real errors).

dilawar/moodle