Add membersrvc/ca/utils.go Tests

[JonathanLevi]

Description

We need to have a set of tests covering the behavior and functionality. In particular, this issue focuses on the shared CA utils.go functions 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

[JonathanLevi]

@srderson Thanks. Let's keep this issue open please (despite merging #2051)