Revert 8.2.0 version change

[ArturT]

Story

https://trello.com/c/tEgpIuOn

Description

This PR reverts changes from 8.2.0 version that have been introduced in:

• Avoid needing a shell to support Distroless Container Images (in most cases) #299

to address the issue reported in:

• 8.2.0 may have a bug #301

But we keep some code simplification:

• Keep Kernel.exec for Spinach to avoid catching the exit code
• Keep: fd13e84 - we removed the unneeded EXTRA_TEST_FILES_DELAY env var in CircleCI yml that was accidentally added some time ago.

---

• You added the changes to the UNRELEASED section of the CHANGELOG.md, including the needed bump (ie, patch, minor, major)
• You follow the architecture outlined below for RSpec in Queue Mode, which is a work in progress (feel free to propose changes):
  • Pure: lib/knapsack_pro/pure/queue/rspec_pure.rb contains pure functions that are unit tested.
  • Extension: lib/knapsack_pro/extensions/rspec_extension.rb encapsulates calls to RSpec internals and is integration and e2e tested.
  • Runner: lib/knapsack_pro/runners/queue/rspec_runner.rb invokes the pure code and the extension to produce side effects, which are integration and e2e tested.