Fix duplicate retention case

[aateeqi]

Description of the issue

[todo] https://github.com/aws/amazon-cloudwatch-agent/issues/554

Description of changes

When the same retention is set multiple times for a log group, retention will be set as long as any file_path is created for that log group.

License

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Tests

Describe what tests you have done.

Requirements

Before commit the code, please do the following steps.

1. Run make fmt and make fmt-sh
2. Run make linter

[codecov-commenter]

Codecov Report

Merging #556 (96c3bce) into master (e571562) will decrease coverage by 0.54%. The diff coverage is 61.90%.

@@            Coverage Diff             @@
##           master     #556      +/-   ##
==========================================
- Coverage   57.15%   56.61%   -0.55%     
==========================================
  Files         362      375      +13     
  Lines       16868    17839     +971     
==========================================
+ Hits         9641    10099     +458     
- Misses       6676     7148     +472     
- Partials      551      592      +41     

Impacted Files	Coverage Δ
logs/logs.go	20.25% <61.90%> (ø)
plugins/inputs/win_perf_counters/pdh.go	65.47% <0.00%> (ø)
translator/util/platform_windows.go	75.00% <0.00%> (ø)
...puts/logfile/tail/file_deleting_checker_windows.go	36.36% <0.00%> (ø)
...gins/inputs/windows_event_log/wineventlog/utils.go	69.60% <0.00%> (ø)
...windows_event_log/wineventlog/wineventlogrecord.go	59.09% <0.00%> (ø)
...gins/inputs/windows_event_log/windows_event_log.go	26.08% <0.00%> (ø)
plugins/inputs/logfile/tail/tail_windows.go	100.00% <0.00%> (ø)
...nputs/windows_event_log/wineventlog/wineventlog.go	36.32% <0.00%> (ø)
... and 7 more

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[SaxyPandaBear]

Is there backwards compatibility with the old way that we configured?

[aateeqi]

We can't afford to break backwards-compatibility. What happens if we take an example config where there's multiple configs pointing to the same log group and only one of the configs has a retention policy (existing behavior)? Can you build this and manually verify that behavior works?

Yes backwards compatibility still maintained: if the customer has multiple streams for a log_group and retention only configured in one, it will still successfully update the retention. Note the 2 configs pointing to the same log group amazon-cloudwatch-agent.log with only 1 of them having retention in days.