Add new ParallelTests::RSpec::VerboseFormatter for enhanced debugging

[jdufresne]

The new formatter allows users of parallel_rspec to more easily obtain detailed information about the examples running as they occur in real time.

Background:

In my project, it was observed that an RSpec example would hang intermittently on CI. At first, no team member was able to make this reliably fail enough on CI to facilitate debugging and no one was able to reproduce locally at all. The hang only occurred with parallel tests running and never with just the "rspec" command.

In an attempt to gather more information, we began using the RSpec "documentation" formatter which outputs the "description", "context", and "it" strings. Unfortunately, when running in parallel, the output from different processes will interleave with one another making it extremely difficult to understand which example is responsible for the observed hang.

Solution:

Build a "documentation-like" formatter that plays nicely with the parallel_tests framework. The new formatter always ouputs all information on a single line to avoid important details from different processes interleaving with one another. This means the "describe" and "context" strings will be repeated across multiple "it" blocks.

To further assist, the formatter include the PID and parallel process number to help identify which subprocess hangs and which one continues. The output will look something like:

[14403] [2] [STARTED] Foo foo
[14402] [1] [STARTED] Bar bar
[14402] [1] [PASSED] Bar bar

In the output above, it is clear the "Foo foo" example is still running.

Using this formatter, our project's team was able to successfully identify the example causing the intermittent hang and then address it. As such, I'm hoping that this may be useful for a larger audience.

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Thank you for your contribution!

Checklist

• Feature branch is up-to-date with master (if not - rebase it).
• Added tests.
• Added an entry to the Changelog if the new
  code introduces user-observable changes.
• Update Readme.md when cli options are changed

[grosser]

awesome, looks nice!