Storwize/SVC: Check wwpn not None

If the storage doesn't have WWPN information for a host but gets it in
the connector, initialize_connection can fail because it does
wwpn.lower(), and wwpn can be None. Make sure it isn't before calling
lower().

Change-Id: I9923f5c87a1e596e35116bfcbf08c181b75bba35
Closes-bug: 1279061

cinder/volume/drivers/ibm/storwize_svc/helpers.py

@@ -200,6 +200,7 @@ class StorwizeHelpers(object):
                         host_name = name
                     elif ('wwpns' in connector and
                           len(connector['wwpns']) and
+                          wwpn and
                           wwpn.lower() in
                           [str(x).lower for x in connector['wwpns']]):
                         host_name = name