Periodic jobs should not have CIFLOW_DEFAULT label (#66300)
Summary:
Noticed that `periodic-pytorch-linux-xenial-cuda10.2-cudnn7-py3-gcc7-slow-gradcheck` job has a `ciflow/default`, but does not have a `ciflow/scheduled` label
Added asserts to enforce that jobs with non-trival is_scheduled property do not have default and do have scheduled labesl
Rename `periodic-pytorch-linux-xenial-cuda10.2-cudnn7-py3-gcc7-slow-gradcheck` to `periodic-linux-xenial-cuda10.2-py3-gcc7-slow-gradcheck`
Fixes #{issue number}
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66300
Reviewed By: seemethere
Differential Revision: D31493323
Pulled By: malfet
fbshipit-source-id: 194c1d7a4e659847d94a547b87a0d7d08e66406d
