Remove CoreOS, add Flatcar (#14796)
Remove CoreOS, add Flatcar (#14796)


brjohnstmsft/azure-rest-api-specs,solankisamir/azure-rest-api-specs,johanste/azure-rest-api-specs,solankisamir/azure-rest-api-specs,AsrOneSdk/azure-rest-api-specs,AppPlatPerf/azure-rest-api-specs,brjohnstmsft/azure-rest-api-specs,naveedaz/azure-rest-api-specs,AsrOneSdk/azure-rest-api-specs,johanste/azure-rest-api-specs,naveedaz/azure-rest-api-specs,AppPlatPerf/azure-rest-api-specs