Second try with this PR: Minor fixes made to improve fault-tolerance

Created by: mguijarr

I am sorry of the inconvenience with the nasty typos and bugs introduced with previous PR. Hopefully this time we have it right...

Please give it a try :)

For get_initial_state : we have to agree on which hardware objects to use for front light and back light, in order to have a common set of referenced hardware objects in the diffractometer object xml. We always had a specific hwobj acting both as an actuator and as a motor AFAIK, I think we should continue with something like that. I have no time at the moment but I will try to have a look very soon, I thought MicrodiffLight was doing the job. Which hardware objects are you using for the front/back lights ? At the moment, I use Mikel's suggestion and I guess it is ok, it should work with our both cases.