[thci] allow REED DUTs to upgrade (#6789)
[thci] allow REED DUTs to upgrade (#6789)

Some Thread 1.2 tests require that REED DUTs upgrade to Router. Allow
it while keeping existent functionality for reference devices.
abtink/openthread,abtink/openthread,srickardti/openthread,jwhui/openthread,jwhui/openthread,openthread/openthread,openthread/openthread,jwhui/openthread,srickardti/openthread,abtink/openthread,jwhui/openthread,openthread/openthread,srickardti/openthread,abtink/openthread,openthread/openthread,srickardti/openthread