tests: fix reporting in network tests
tests: fix reporting in network tests

Do not trash stdout with VM's command output. Log it as part of
(potential) failure message.

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