app: add missing setters for default_pool* global properties
app: add missing setters for default_pool* global properties

Function itself was already written, but not set in the properties.

QubesOS/qubes-issues#2256

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