Fixed the issue that the pod could not start mounting pvc when the prefix parameter contained a slash "/"

[gsmini]

when use

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: s3-sc-custom-dir
provisioner: ch.ctrox.csi.s3-driver
parameters:
  mounter: s3fs
  bucket: my-bucket
  usePrefix: "true"
  prefix:  userid/1/order
  csi.storage.k8s.io/provisioner-secret-name: csi-s3-secret
  csi.storage.k8s.io/provisioner-secret-namespace: kube-system
  csi.storage.k8s.io/controller-publish-secret-name: csi-s3-secret
  csi.storage.k8s.io/controller-publish-secret-namespace: kube-system
  csi.storage.k8s.io/node-stage-secret-name: csi-s3-secret
  csi.storage.k8s.io/node-stage-secret-namespace: kube-system
  csi.storage.k8s.io/node-publish-secret-name: csi-s3-secret
  csi.storage.k8s.io/node-publish-secret-namespace: kube-system

the prefix contains slash "/", so pod run err with:

 Warning  FailedMount      10s (x7 over 42s)  kubelet         MountVolume.MountDevice failed for volume "pvc-6b77ca3b-a2ca-4053-9f95-ae2ca593285a" : rpc error: code = Unknown desc = The specified key does not exist.

this issue has the same question : #56

i debug and found the reason:

func volumeIDToBucketPrefix(volumeID string) (string, string) {
	// if the volumeID has a slash in it, this volume is
	// stored under a certain prefix within the bucket.
	splitVolumeID := strings.Split(volumeID, "/")
	if len(splitVolumeID) > 1 {
		return splitVolumeID[0], splitVolumeID[1]
	}

	return volumeID, ""
}

https://github.com/ctrox/csi-s3/blob/master/pkg/driver/controllerserver.go#L265

this code split the prefix and splitVolumeID[0] is bucket name, splitVolumeID[1] is not the subpath when prefix contains slash “/” ：

splitVolumeID := strings.Split(volumeID, "/")

so i fix it ,just like this:

func volumeIDToBucketPrefix(volumeID string) (string, string) {
	// if the volumeID has a slash in it, this volume is
	// stored under a certain prefix within the bucket.
	splitVolumeID := strings.SplitN(volumeID, "/", 2)
	if len(splitVolumeID) > 1 {
		return splitVolumeID[0], splitVolumeID[1]
	}

	return volumeID, ""
}