Storwize SVC driver hostname can't start with number

Storwize family storage does not allow host identifier start with
a numeric number. Otherwise cinder initialize_connection() API will
throw exception due to such invalid host name in the connector. The fix
is to add a '_' symbol as prefix if the host identifier in connector
starts with non-alphabet letters.

Closes-Bug: #1233952
Change-Id: Ia88afc373e2635c10c3f6256331a4fd90f51f4b8

cinder/volume/drivers/storwize_svc.py

@@ -482,6 +482,11 @@ def _connector_to_hostname_prefix(self, connector):
             raise exception.NoValidHost(reason=msg)
 
         host_name = str(host_name)
+
+        # Storwize family doesn't like hostname that starts with number.
+        if not re.match('^[A-Za-z]', host_name):
+            host_name = '_' + host_name
+
         return host_name[:55]
 
     def _find_host_from_wwpn(self, connector):