Backfill unit coverage for cf help
Backfill unit coverage for cf help

We had a pull request that added `delete` to the help text, and while
reviewing that PR we noticed that no tests were failing nor did any need
modification. We've added more thorough coverage and made the assertions
more consistent.

[Finishes #161739215]

Co-authored-by: Jen Spinney <a20f9e7a68b0510792107656332d0b79d5e0f8f7@pivotal.io>

cloudfoundry/cli,cloudfoundry/cli,cloudfoundry/cli