etcd: Document the container test
etcd: Document the container test

It was hard to follow what functionality it was testing, and what the
expected behavior was.

NetSys/quilt,LuiseV/quilt,LuiseV/quilt,kelda/kelda,NetSys/quilt,kelda/kelda,quilt/quilt,kklin/quilt,LuiseV/quilt,NetSys/quilt,LuiseV/quilt,NetSys/quilt,quilt/quilt,kklin/kelda,kelda/kelda,LuiseV/quilt,kklin/kelda,NetSys/quilt,kklin/kelda,kklin/quilt,kklin/quilt,kklin/kelda,quilt/quilt,kklin/quilt,quilt/quilt,kelda/kelda