when using -i"hostname," on the cli - don't complain about the host named "" not being a host - just clip it from the list

lib/ansible/inventory/__init__.py

@@ -53,6 +53,7 @@ class Inventory(object):
         if type(host_list) in [ str, unicode ]:
             if host_list.find(",") != -1:
                 host_list = host_list.split(",")
+                host_list = [ h for h in host_list if h and h.strip() ]
 
         if type(host_list) == list:
             all = Group('all')