IsRancher checks if volume driver is rancher managed driver.

IsRancherVolume checks if a volume to be considered as a flex volume if it is in rancherDrivers and the capability is flex raise an error if its rancher-managed driver but the socket file is not available.

Capability represents the list of capabilities a volume driver can return.

Response is the strucutre that the plugin's responses are serialized to.

Volume represents a volume object for use with `Get` and `List` requests.