py33: don't encode security_group

In Python 3, str and bytes can not be mixed. str.encode() will
return bytes in py33, which will induce the mismatch.

Bypass the s.name.encode() in py33.

Change-Id: Iee8d69aab9df4af126e94e4363f79e32fdd70fcd
Close-bug: #1231868
Merge "py33: don't encode security_group"