Longhorn - v0.3.0

Docker images for this release:

Longhorn manager: rancher/longhorn-manager:v0.3.0
Longhorn engine: rancher/longhorn-engine:v0.3.0
Longhorn UI: rancher/longhorn-ui:v0.3.0

Features in this release: * Upgrade support
* Engine upgrade - Engine can be upgraded from v0.3 to v0.3+ without volume downtime. Upgrading from v0.2 to v0.3 would incur volume downtime.
* Manager upgrade - Manager can be upgraded from previous release, with API downtime. No downtime for the Longhorn volumes (except from v0.2 to v0.3). * Container Storage Interface(CSI) - Support CSI as the Kubernetes storage driver for Kubernetes v1.10+. It will eventually replaced our Flexvolume driver in the future. * S3 backup target - Support S3 as the backup target. * iSCSI endpoint - Support iSCSI as an alternative volume frontend. * Base image - Support using RancherVM base image to be used as the base for the volume, so the user will able to start a VM using Longhorn volume as root image. * RancherVM live migration - Support RancherVM live migration with Longhorn volume as the root image. * Multiple disk with capacity based scheduling - User can update the node config and set desired disk (mounted to a node directory) to store Longhorn volume data. Longhorn can choose where to place the volume data depends on how much space the disk had left. * Websocket support - UI will get the up to date information without refreshing.