significant code refactoring

[alexei-led]

• use golangci-lint linter
• fix violations for multiple linters
• align CLI flag names (no Camel case)
• use time.Duration for duration CLI flags
• remove unused code
• refactor code to reduce duplications

[codecov-commenter]

Codecov Report

Merging #211 (9a13db7) into master (ddb0ce3) will decrease coverage by 1.90%.
The diff coverage is 20.70%.

@@            Coverage Diff             @@
##           master     #211      +/-   ##
==========================================
- Coverage   42.01%   40.11%   -1.91%     
==========================================
  Files          37       37              
  Lines        1478     1249     -229     
==========================================
- Hits          621      501     -120     
+ Misses        857      748     -109     

Impacted Files	Coverage Δ
pkg/chaos/command.go	0.00% <0.00%> (ø)
pkg/chaos/docker/cmd/exec.go	16.66% <0.00%> (+2.38%)	⬆️
pkg/chaos/docker/cmd/kill.go	14.28% <0.00%> (ø)
pkg/chaos/docker/cmd/pause.go	14.28% <0.00%> (ø)
pkg/chaos/docker/cmd/remove.go	14.28% <0.00%> (+1.78%)	⬆️
pkg/chaos/docker/cmd/restart.go	16.66% <0.00%> (+3.33%)	⬆️
pkg/chaos/docker/cmd/stop.go	12.50% <0.00%> (ø)
pkg/chaos/netem/cmd/corrupt.go	11.76% <0.00%> (+2.67%)	⬆️
pkg/chaos/netem/cmd/delay.go	10.52% <0.00%> (+2.19%)	⬆️
pkg/chaos/netem/cmd/duplicate.go	11.76% <0.00%> (+2.67%)	⬆️
... and 32 more

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