Fix broken datasource tests

A follow-up for #449.

 - Reenable `beforeEach(given.emptyWorkspace)`.

 - Modify `given.emptyWorkspace` to increase the hook timeout
   in order to prevent timeouts on slow CI build slaves.

 - Remove checks for `config` property that does not exist in
   datasources. It used to be a problem in models, I suspect the checks
   very copied over.

/to @seanbrookes please review