qubesvm: fix stdio handling in vm.run_service_for_stdio
qubesvm: fix stdio handling in vm.run_service_for_stdio

Do set stdin/stdout/stderr descriptors as PIPE. Otherwise would not be
redirected.

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