[WIP] Add initial maintenance mode test

[eriknordmark]

trafficstars

Have issues that the status from the device does not appear in the test.

The idea is to evolve the test (once it can toggle maintenance_mode) to check that config changes will be ignored by the device but that the device can be rebooted while it is in maintenance mode.

[mydatascience]

Should we do something with this PR? @eriknordmark

[uncleDecart]

@eriknordmark will there be any updates on that or can we close this PR?