Insteon_Thermo: Process Device Cmd Stack on Msg Ack

Failed to include proper calls to _process_command_stack in the Insteon::Thermostat::_process_message routine.

This likely has little effect on i2CS thermostats that had broadcast messages enabled because the thermostat immediatley issued a broadcast command which would cause MH to process the command stack.

However, i1 devices or i2cs devices without broadcast enabled, may have become "locked up" within MH after the issuance of a setpoitn change.