Add messages to VM model

Add messages keeping most similar to XenServer api, including
parameters names

Some classes were forcing some parameters to XenServer, I just left
them needing to be explicit passed, if we define its better assume
some default values, no problem
@fernandes I was willing to do this but i think we should not do this move until we remove the `Xenserver` code from the main gem and deprecate this param.
I worry that someone might have some legacy code that rely on this param.