Improve error message when using self-signed certificate

[szh]

Desired Outcome

Conjur CLI message when not using --self-signed with self signed cert should be improved

Implemented Changes

• In the init command, if there's an error retrieving or validating the server certificate, and the --self-signed flag is not provided, print "If you're attempting to use a self-signed certificate, re-run the init command with the --self-signed flag"

Connected Issue/Story

CyberArk internal issue ID: CNJR-506

Definition of Done

At least 1 todo must be completed in the sections below for the PR to be merged.

Changelog

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

Test coverage

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

Documentation

• [ ] Docs (e.g. READMEs) were updated in this PR
• [ ] A follow-up issue to update official docs has been filed here: [insert issue ID]
• [x] This PR does not require updating any documentation

Behavior

• [x] This PR changes product behavior and has been reviewed by a PO, or
• [ ] These changes are part of a larger initiative that will be reviewed later, or
• [ ] No behavior was changed with this PR

Security

• [ ] Security architect has reviewed the changes in this PR,
• [ ] These changes are part of a larger initiative with a separate security review, or
• [x] There are no security aspects to these changes

[codeclimate[bot]]

Code Climate has analyzed commit 2c6bf5bc and detected 1 issue on this pull request.

Here's the issue category breakdown:

Category	Count
Style	1

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 81.0% (0.0% change).

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