Create a contract enforcement layer

[nuwang]

Something that would be desirable is a cloudbridge-wide, "contract enforcement layer", that operates above the individual providers. This layer could do provider-independent contract enforcement, like ensuring parameter combinations make sense, that all method calls are logged, that exceptions are wrapped etc. before and after calling the provider implementation layer. At present, we do not have this capability, meaning that a lot of logic is duplicated, and some common things are harder to enforce (e.g. name validation, logging, exception handling)

We can probably do some variant of: https://github.com/gvlproject/cloudbridge/issues/9#issuecomment-326101464 to accomplish this, but we probably need to make sure this happens for the 1.0.0 release.