Fix flakiness in sink/cache/impl_test.go
Fix flakiness in sink/cache/impl_test.go

taimir/heapster,krzyzacy/heapster,aegixx/heapster,Stackdriver/heapster,thucatebay/heapster,huangyuqi/heapster,liuhewei/heapster,shilpamayanna/heapster,vicki-c/heapster,piosz/heapster,mdshuai/heapster,vishh/heapster-1,naxhh/heapster,shilpamayanna/heapster,a-robinson/heapster,mwielgus/heapster,mdshuai/heapster,digideskio/heapster,afein/heapster,skytap/heapster,vicki-c/heapster,whuwxl/heapster,jackzampolin/heapster,AlmogBaku/heapster,andyxning/heapster,johanneswuerbach/heapster,Huawei-PaaS/heapster,vishh/heapster-1,burmanm/heapster,bluebreezecf/heapster,Huawei-PaaS/heapster,mwielgus/heapster,adfin/statster,johanneswuerbach/heapster,titilambert/heapster,whuwxl/heapster,saiwl/heapster,liubog2008/heapster,luxas/heapster,krzyzacy/heapster,andyxning/heapster,saiwl/heapster,mwringe/heapster,naxhh/heapster,a-robinson/heapster,skytap/heapster,ravihansa3000/heapster,ravihansa3000/heapster,afein/heapster,jackzampolin/heapster,luxas/heapster,digideskio/heapster,liubog2008/heapster,bluebreezecf/heapster,burmanm/heapster,thucatebay/heapster,adfin/statster,taimir/heapster,liuhewei/heapster,mwringe/heapster,piosz/heapster,wulonghui/heapster,bruceauyeung/heapster,bruceauyeung/heapster,Stackdriver/heapster,huangyuqi/heapster,aegixx/heapster,wulonghui/heapster,AlmogBaku/heapster,titilambert/heapster