Run external cluster tests with multiple databases

[zuiderkwast]

Change the runtest flag --cluster-mode to no longer imply --single-db. This allows more tests to run against an external node running in cluster mode.

Also fix incorrectly tagged tests so that ./runtest --singledb passes locally.

Without this change, this doesn't pass because several tests are incorrectly tagged as external:skip instead of singledb:skip or cluster:skip. In the CI, we apparently only run with singledb when implied by --cluster-mode (until now), which we only use in the external cluster mode test. That's why the incorrect tags were not detected.

• singledb:skip is used for tests that do select and assume that a client has selected db 9.
• cluster:skip is used when the test uses SWAPDB, cross-slot commands other things forbidden in cluster mode.

Additional fix: End tests with a linebreak when running with the --fastfail flag. A program that doesn't end its output with a linebreak annoys the prompt in the terminal.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.37%. Comparing base (5cc2b25) to head (846cd29).
Report is 7 commits behind head on unstable.

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #2176      +/-   ##
============================================
- Coverage     71.50%   71.37%   -0.14%     
============================================
  Files           122      122              
  Lines         66452    66452              
============================================
- Hits          47515    47428      -87     
- Misses        18937    19024      +87     

see 11 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.