Error reporting via flexvolume isn't great

[alaric-dotmesh]

I had a problem with mounting a volume from a dot under k8s.

What I saw was /var/log/dotmesh-flexvolume.log containing repeated:

9911: 2018/02/21 10:47:42.292303 MOUNT: targetMountDir: /var/lib/kubelet/pods/5aa672df-16f4-11e8-bfa1-e61bd8f258e6/volumes/dotmesh.io~dm/pvc-5aa52e60-16f4-11e8-bfa1-e61bd8f258e6, jsonOptions: {"kubernetes.io/fsType":"zfs","kubernetes.io/pod.name":"redis-7d85fc658d-sd7sn","kubernetes.io/pod.namespace":"default","kubernetes.io/pod.uid":"5aa672df-16f4-11e8-bfa1-e61bd8f258e6","kubernetes.io/pvOrVolumeName":"pvc-5aa52e60-16f4-11e8-bfa1-e61bd8f258e6","kubernetes.io/readwrite":"rw","kubernetes.io/serviceAccount.name":"default","name":"moby_counter2@newbranch","namespace":"admin","subdot":""}
29911: 2018/02/21 10:47:58.023588 RPC FAIL: {Namespace:admin Name:moby_counter2@newbranch Subdot:__default__} -> DotmeshRPC.Procure -> A volume called admin/moby_counter2 already exists with id b50d97a7-78ff-4fae-7ed1-8305e42d452a

But docker logs dotmesh-server-inner finall revealed the real problem was:

Error procuring filesystem: Cannot use branch-pinning syntax (docker run -v volume@branch:/path) to create a non-existent volume with a non-master branch, pausing and trying again...