:include, :verbose, no rebuild on caps and all boxes support

Original `oxdi/vagrant-nixos` does not support boxes that were not explicitly prepared for using with this extension. 

This fix adds :include option, to make provisioning available for incompatible boxes (all others).

Work around implemented through explicit include of option of nixos-config with `-I nixos-config= flag` added to `nixos-rebuild switch` command.

Also added :verbose option, to show whole provisioning log.

And it does not do explicit environment rebuild on every capability call as they are immutable. They required some lazy eval mech.