Update the location of the LH driver

When the lefthand driver was pulled from nova into cinder, the
volume_driver location was incorrect. The migration mapped the old
location to the new location;
cinder.volume.drivers.san.HpSanISCSIDriver
This patch is just updating the docs to the correct location.

Change-Id: I60275ee4eb680e479231d94282d2c0731b672946
Merge "Update the location of the LH driver"