Add test whether all providers in providers.yml are present

[mjuenema]

Dynamically eval() instantiating every provider and check whether there is at least one class for each provider in terrascript.data and terrascript.resource.

[ilons]

This might prove problematic, as not all providers are actually having classes generated.
That could be a bug in the code generation, a legit case where there is no data classes for a provider, or an updated (remove) provider code which is no longer parsing properly.

I have the same issue with #108, where Microsoft simply re-organized the code for the provider so that we can no longer parse it, which in itself is not a bug. If we add a test for this, then it would fail for some providers, while we cant really do anything to fix the issue (short-term).