Improve the stability of e2e tests

[nolar]

Part of an effort to make Kopf-based operators more stable and resilient.

Issue : #13 #142

Description

E2E tests are flaky and unstable. This PR makes them more stable by:

• Running in a standalone mode (on the same minikube as other, probably failed tests — to prevent freezing for minutes).
• Limiting a time of termination of a background operator to 60s (and adding this feature).
• Using a dynamic pod name in the pod-involving e2e tests (otherwise, it hits "409 Conflict" — when the pod already exists in the same cluster (actual for the local runs)).

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• Refactor/improvements

[zincr]

🤖 zincr found 0 problems , 0 warnings

✅ Large Commits
✅ Approvals
✅ Specification
✅ Dependency Licensing

[zincr]

🤖 zincr found 1 problem , 0 warnings

❌ Approvals
✅ Large Commits
✅ Specification
✅ Dependency Licensing

Details on how to resolve are provided below

---

Approvals

All proposed changes must be reviewed by project maintainers before they can be merged

Not enough people have approved this pull request - please ensure that 1 additional user, who have not contributed to this pull request approve the changes.

• ✅ Approved by PR author @nolar
• ❌ 1 additional approval needed
   

[codecov-io]

Codecov Report

Merging #149 into master will decrease coverage by 0.01%.
The diff coverage is 86.2%.

@@            Coverage Diff             @@
##           master     #149      +/-   ##
==========================================
- Coverage   83.55%   83.54%   -0.02%     
==========================================
  Files          30       30              
  Lines        1545     1544       -1     
  Branches      227      227              
==========================================
- Hits         1291     1290       -1     
  Misses        209      209              
  Partials       45       45

Impacted Files	Coverage Δ
kopf/testing/runner.py	81.33% <86.2%> (-0.25%)	⬇️

[codecov-io]

Codecov Report

Merging #149 into master will decrease coverage by 0.01%.
The diff coverage is 86.2%.

@@            Coverage Diff             @@
##           master     #149      +/-   ##
==========================================
- Coverage   83.55%   83.54%   -0.02%     
==========================================
  Files          30       30              
  Lines        1545     1544       -1     
  Branches      227      227              
==========================================
- Hits         1291     1290       -1     
  Misses        209      209              
  Partials       45       45

Impacted Files	Coverage Δ
kopf/testing/runner.py	81.33% <86.2%> (-0.25%)	⬇️