Fix compatibility with Python 3.7

Simply replace the raise statement with return. All tests pass with
Python 3.7.0 here with the change.

Author: felixonmars

SoftLayer/API.py

@@ -298,7 +298,7 @@ def iter_call(self, service, method, *args, **kwargs):
                     results = transports.SoftLayerListResult(results, len(results))
                 else:
                     yield results
-                    raise StopIteration
+                    return
 
             for item in results:
                 yield item
@@ -313,8 +313,6 @@ def iter_call(self, service, method, *args, **kwargs):
 
             offset += limit
 
-        raise StopIteration
-
     def __repr__(self):
         return "Client(transport=%r, auth=%r)" % (self.transport, self.auth)