block-snapshot: set qubes.xml path for test VMs
block-snapshot: set qubes.xml path for test VMs

Since it is running with totally different environment, QUBES_XML_PATH
isn't passed from test runner. Apply heuristic based on VM name.

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