Fix flakiness in cache/impl_test
Fix flakiness in cache/impl_test

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