[BUGFIX] generateUUID() creates uppercase characters in UUIDs
The UUIDs generated by that method were always lowercase, now they are
uppercase (since change I1237fdfbee75cbfca2f2082cf30a69383dbc7fd5). As
soon as you do a case-sensitive comparison on those UUIDs as strings,
this will now break, even if the UUIDs are the same semantically.
This change makes them lowercase again.