Do not use prefix to lookup host in Storwize/SVC.

Do not use prefix to lookup host in Storwize/SVC.

Currently, the Storwize/SVC driver creates a host name prefix for host
objects on the back-end, and uses that to look up hosts. However, if a
host was already created with a different name (for example, manually
by an admin), the host creation operation will fail, as a host with
that connection information already exists. Instead, we look up a host
based on available connection information.

Fixes bug: 1149072

Change-Id: I336dbea85bfaf928a550a15d177e2b9b0ffd38bf