[qubes-template-kali] Installation fails with 'disk quota exceeded' error

Thanks a lot for the quick changes @fepitre

I have to hint that the default template root size will be exceeded by kali-linux-everything.

Template disk useage (compared to core)
kali-linux-core ± 0,0 GiB
kali-linux-default + 5,54 GiB
kali-linux-everything + 16,7 GiB

Something like

ifeq ($(TEMPLATE_FLAVOR), kali+everything)
  TEMPLATE_ROOT_SIZE = 30G
endif

could be necessary. (I do not think that many reasonable people use the everything installation; but in case there are any, this may be changed.)