问题现象：
执行 cloud-init 报错：Requirement.parse('six>=1.11.0')
原因：
Python 的模块 six 依赖版本太低
[root@VM_0_9_centos cloud-init-17.1]# cloud-init
Traceback (most recent call last):
File "/usr/bin/cloud-init", line 5, in <module>
from pkg_resources import load_entry_point
File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 3011, in <module>
parse_requirements(__requires__), Environment()
File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 630, in resolve
raise VersionConflict(dist,req) # XXX put more info here
pkg_resources.VersionConflict: (six 1.9.0 (/usr/lib/python2.7/site-packages), Requirement.parse('six>=1.11.0'))
解决方案：
升级 six 模块版本即可
pip install --upgrade six
