propagator-20150306-alt1 and make-initrd-propagator-0.25-alt1
have made it actually possible to use resulting LiveCD images
along with USB flash media to achieve data persistence that's
been long available for BIOS boot mode (see also #28289).

This isn't perfect but let's try flipping the switch:
all desktop regular builds are now "live_rw" by default
in EFI mode.

This requires mkimage >= 0.2.17.