tests: correctly compare DeviceManager objects
tests: correctly compare DeviceManager objects

Usefull for assertEqual(vm1.devices, vm2.devices) - clone tests, backup
tests etc.

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