Update the HP 3PAR default persona

This updates the change in the OpenStack Configuration Reference Guide to
match the merged code (https://review.openstack.org/118500).
The new default for the hp3par:persona should be '2 - Generic-ALUA'.

Change-Id: I4d79ed62a6fe6ed09231b584c96b7a552ee2fb6e
Closes-bug: 1365696
Merge "Update the HP 3PAR default persona"