Add edge-case scenario handling in getLogLevel

[sameersubudhi]

What was the problem?

This PR resolves #208

How was it solved?

• Add error handling for missing scenarios
• Add unit tests
• Update Lisk Core v4 install command to install v4.0.1 or later
• Bump version to 2.0.1

How was it tested?

• yarn test config
• Retested migrator e2e against the mainnet:
  • ./bin/run -s 23362048 -d ~/mainnet-v3 -c ./custom-config.json --auto-migrate-config --auto-start-lisk-core-v4

[codecov]

Codecov Report

Merging #209 (c3d7aca) into development (8381088) will decrease coverage by 0.02%.
The diff coverage is 83.33%.

Additional details and impacted files

@@               Coverage Diff               @@
##           development     #209      +/-   ##
===============================================
- Coverage        82.15%   82.13%   -0.02%     
===============================================
  Files               25       25              
  Lines              818      823       +5     
  Branches           120      124       +4     
===============================================
+ Hits               672      676       +4     
- Misses             146      147       +1     

Files	Coverage Δ
src/utils/config.ts	98.50% <100.00%> (+0.04%)	⬆️
src/utils/node.ts	43.58% <50.00%> (-0.38%)	⬇️

[nagdahimanshu]

LGTM 👍