Implements role parameter in check command in CLI

[juniortaeza]

Desired Outcome

Depends on conjur-api-go#153

This pull request adds a role parameter to the 'check' command for the Go CLI.

Implemented Changes

• Updated 'check' to include role flag
• Updated check_tests to test full API & CLI functionality of flag and command

Definition of Done

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

Changelog (need a Changelog)

• The CHANGELOG has been updated, or
• 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
• 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
• This PR does not require updating any documentation

Behavior

• 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
• There are no security aspects to these changes

[szh]

Looks good. Just needs a rebase

[szh]

LGTM, needs a rebase.

[codeclimate]

Code Climate has analyzed commit 9b48fee and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 92.8% (50% is the threshold).

This pull request will bring the total coverage in the repository to 69.2% (0.2% change).

View more on Code Climate.

[szh]

LGTM!