Add error handling when user uses older conjurrc

[sigalsax]

What does this PR do?

When a user doesn't have the correct keys in their conjurrc config file (because of an older version of conjurrc when using the ruby cli), the user gets incomprehensive error. This fixes this by adding error handling and returning a more detailed error message.

Previously:

With this change:

What ticket does this PR close?

Resolves #292

Checklists

Change log

• [ ] The CHANGELOG has been updated, or
• [x] This PR does not include user-facing changes and doesn't require a CHANGELOG update

Test coverage

• [ ] This PR includes new unit and integration tests to go with the code changes, or
• [x] The changes in this PR do not require tests

Documentation

• [ ] Docs (e.g. READMEs) were updated in this PR, and/or there is a follow-on issue to update docs, or
• [x] This PR does not require updating any documentation

[codeclimate[bot]]

Code Climate has analyzed commit 20af78c8 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 92.8% (75% is the threshold).

This pull request will bring the total coverage in the repository to 89.7% (0.0% change).

View more on Code Climate.