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
Merge "Storwize/SVC: Check wwpn not None"