Refactor deploy rake task

Refactor deploy rake task

- Drop auto-deploy pipeline code sections that are now handled
  by the Delivery team's co-ordinated pipelines
- Remove code relevant to Ubuntu 16.04 whose support was
  dropped some time ago
- Improves the deploy related rspec tests
- Exit deploy code earlier when possible similar to how
  logic gates are handled in other rake tasks

Signed-off-by: Balasankar "Balu" C <balasankar@gitlab.com>

What does this MR do?

1. Use next to exit early from Rake task - https://stackoverflow.com/a/2316518. This is what we do in other rake tasks too.
2. Drop the auto-deploy related branch of deploy codebase. Deploys of auto-deploy packages are now handled by Delivery team's coordinated pipeline. Moreover, the code being removed would run only as part of Ubuntu 16.04 staging upload, which has been removed for few months now.

Related issues

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• MR title and description are up to date, accurate, and descriptive.
• MR targeting the appropriate branch.
• Latest Merge Result pipeline is green.
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow.

For GitLab team members

If you don't have access to this, the reviewer should trigger these jobs for you during the review process.

• The manual Trigger:ee-package jobs have a green pipeline running against latest commit.
• If config/software or config/patches directories are changed, make sure the build-package-on-all-os job within the Trigger:ee-package downstream pipeline succeeded.
• If you are changing anything SSL related, then the Trigger:package:fips manual job within the Trigger:ee-package downstream pipeline must succeed.
• If CI configuration is changed, the branch must be pushed to dev.gitlab.org to confirm regular branch builds aren't broken.

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes.
• Documentation created/updated.
• Tests added.
• Integration tests added to GitLab QA.
• Equivalent MR/issue for the GitLab Chart opened.
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.