Enable LGTM checks and fix few LGTM alerts

[nolar]

What do these changes do?

Improve the codebase to resolve the remaining LGTM's warnings and some of the recommendations.

LGTM itself is enabled via GitHub actions/integrations, so no code changes are needed.

Description

LGMT is a code quality control tool (one of them) — as in "looks good to me": https://lgtm.com/

This project's analysis can be previewed at https://lgtm.com/projects/g/zalando-incubator/kopf/

The code logic is changed in few places — presumably, with no behavioural changes (just try-except-else restructuring to a flat code).

Issues/PRs

Issues: #13

Type of changes

• Mostly CI/CD automation, contribution experience

Checklist

• The code addresses only the mentioned problem, and this problem only
• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt

[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

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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
   

[lgtm-com]

This pull request fixes 10 alerts when merging 74ee728 into 3614ee4 - view on LGTM.com

fixed alerts:

• 6 for Unused local variable
• 3 for Unnecessary 'else' clause in loop
• 1 for Except block handles 'BaseException'

[lgtm-com]

This pull request fixes 10 alerts when merging 0074b96 into 3614ee4 - view on LGTM.com

fixed alerts:

• 6 for Unused local variable
• 3 for Unnecessary 'else' clause in loop
• 1 for Except block handles 'BaseException'