tests: convert tests/int/basic to core3 API
tests: convert tests/int/basic to core3 API

Not all tests converted - some of them will be removed in the next
commit. Also it doesn't mean that all tested functionality already
works...

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