Fix: Ensure GCP tests don't fail on slow connection; add missing Service test cases

[cortadocodes]

Contents

Minor fixes and improvements

• Add ability to delete topic and subscription when a Service has finished serving
• Facilitate graceful exit for serving Services on KeyboardInterrupt

Testing

• Test that children can question their own children as part of answering a question
• Close Ensure test topics and subscriptions are deleted even on test failure #94 - delete topics and subscriptions at the end of each test
• Remove timeouts from tests and replace with thread executor shutdown upon test pass, meaning that tests that connect to Google Pub/Sub won't fail because the connection is slower than expected

[codecov-io]

Codecov Report

Merging #93 (a5514cc) into release/0.1.9 (25da590) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@                Coverage Diff                @@
##           release/0.1.9      #93      +/-   ##
=================================================
+ Coverage          96.36%   96.37%   +0.01%     
=================================================
  Files                 51       51              
  Lines               1100     1104       +4     
=================================================
+ Hits                1060     1064       +4     
  Misses                40       40              

Impacted Files	Coverage Δ
octue/cli.py	97.29% <100.00%> (+0.03%)	⬆️
.../resources/communication/google_pub_sub/service.py	100.00% <100.00%> (ø)

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