Fix host option isn't set when using multiple backend

When using multiple volume backend, and volume driver is
cinder.volume.drivers.block_device.BlockDeviceDriver, host
option isn't set so a call to get volumes of a host returns none,
This patch changes to use self.host instead of self.configuration.host

Change-Id: Ide34ed29adad14b778b1a7388e9dc313241fa243
Closes-Bug: 1332909
Merge "Fix host option isn't set when using multiple backend"