codecov: Tweak ignore directive
codecov: Tweak ignore directive

We were covering both etcd_mock.go and quilt-tester, neither of which
users interact with, and thus should be excluded.

kklin/quilt,quilt/quilt,ejj/quilt-dev,ejj/quilt-dev,kklin/kelda,kayousterhout/quilt,ejj/quilt-dev,quilt/quilt,kklin/quilt,NetSys/quilt,kklin/kelda,kayousterhout/quilt,kelda/kelda,quilt/quilt,ejj/quilt-dev,NetSys/quilt,kklin/quilt,kklin/kelda,kayousterhout/quilt,LuiseV/quilt,kklin/kelda,NetSys/quilt,LuiseV/quilt,LuiseV/quilt,LuiseV/quilt,kklin/quilt,kelda/kelda,kelda/kelda,kayousterhout/quilt,NetSys/quilt,quilt/quilt,kelda/kelda,NetSys/quilt,LuiseV/quilt