Execute single iteration of a data driven feature

Originally reported on Google Code with ID 356

Would like to have the possibility to call/execute a data driven feature as a single
iteration.. in other words to call it as a normal method and bypass the data provider
logic. 
I used a couple of hacks for doing achieving this, like:
 calling the generated feature method (ex. some_spec.$spock_feature_3_0(params...))
but this does not play well with shared instances. 
 another one was to use a customized ParameterizedSpecRunner and using        feature.getDataProcessorMethod().setReflection,
feature.getDataProviders().get(0).getDataProviderMethod().setReflection in an ISpecRunner
to hack the data provider state, this is really ugly and error prone.

I need this to easily aggregate and compose data driven features. For example I can
have a spec that tests authentication for different kinds of users and another one,
that depends on a kind of user being authenticated, that tests authorization and some
business flow spec that depends on a user being authorized to execute it. My business
spec would have a setup in which it calls authorizeSpec.authorizeSomeActions, in turn
 authorizeSomeActions would contain a setup that calls authenticateSpec.someUser

Reported by sebi@c4media.com on 2014-03-30 19:43:18

Read the generated feature method and the ParameterizedSpecRunner and ISpecRunner paths mentioned in the report, including their data processor and data provider handling. Trace how shared instances are managed during data-driven execution. Done means a single iteration can be invoked without the data provider hacks and still behaves correctly with shared instances.