[-] fix instance_up metric, closes #759

[pashagolub]

Remove extra setInstanceUpDownState() from Prometheus sink. Add reaper.GetInstanceUpMeasurement() function and use it in FetchMetric()

[coveralls]

Pull Request Test Coverage Report for Build 15557339569

Details

• 0 of 32 (0.0%) changed or added relevant lines in 2 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.3%) to 60.5%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
internal/reaper/database.go	0	10	0.0%
internal/reaper/reaper.go	0	22	0.0%

Files with Coverage Reduction	New Missed Lines	%
internal/reaper/reaper.go	2	0.0%

Totals
Change from base Build 15541270178:	0.3%
Covered Lines:	2688
Relevant Lines:	4443

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💛 - Coveralls