CSI ephemeral volumes: use fixed size

With storage capacity simulation enabled, trying to create ephemeral
volumes with the default maximum volume size may have failed:

  Warning  FailedMount  6s (x5 over 14s)  kubelet            MountVolume.SetUp failed for volume "ephemeral-volume" : rpc error: code = ResourceExhausted desc = not enough capacity: have 100Gi, need 1Ti

Using a smaller size is better because then more than one volume can
be created per host. Even better would be to also add a parameter for
it, but that can be added later.

pkg/hostpath/nodeserver.go

@@ -64,7 +64,9 @@ func (hp *hostPath) NodePublishVolume(ctx context.Context, req *csi.NodePublishV
 		volID := req.GetVolumeId()
 		volName := fmt.Sprintf("ephemeral-%s", volID)
 		kind := req.GetVolumeContext()[storageKind]
-		vol, err := hp.createVolume(req.GetVolumeId(), volName, maxStorageCapacity, mountAccess, ephemeralVolume, kind)
+		// Configurable size would be nice. For now we use a small, fixed volume size of 100Mi.
+		volSize := int64(100 * 1024 * 1024)
+		vol, err := hp.createVolume(req.GetVolumeId(), volName, volSize, mountAccess, ephemeralVolume, kind)
 		if err != nil && !os.IsExist(err) {
 			glog.Error("ephemeral mode failed to create volume: ", err)
 			return nil, err