[#66596670] move FakeClock into separate file (for sharing with other tests)
[#66596670] implement captor lib
[#66596670] moved test helpers into separate files
[#66596670] captor reports heartbeat metrics

Signed-off-by: Johannes Petzold <jpetzold@pivotallabs.com>
[#66596670] add CpuTracker

Signed-off-by: Johannes Petzold <jpetzold@pivotallabs.com>
[#66596670] integrate CpuTracker

Signed-off-by: Johannes Petzold <jpetzold@pivotallabs.com>
[#66596670] go fmt