qmemman: calculate dom0 maxmem properly
qmemman: calculate dom0 maxmem properly

In fact, set to ALL_PHYS_MEM (and the same for other domains that do not
have static-max key, although there should not be any). Previous method
of using maxmem_kb was broken, as qmemman sets maxmem_kb to the memory target
(which I do not like btw).

woju/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin