Add Attribute (CA) feature tests

[JonathanLevi]

Description

We need to have a set of tests covering the behavior and functionality using various (Behave) scenarios around Enrollment.

In particular, with a focus on the Attribute CA (ACA) functionality of Membership Services.

Motivation

At this point, even a small number of positive- and negative- flows will go a long way, both for development, testing but also as an easy way for new users to learn about Hyperledger fabric and its capabilities.

Context

Membership Services end-to-end integration tests. A sub-task of 1575