CreateInstance的datadisk参数单位改为10G，方便计费处理
Merge pull request #6 in SA/mcsapi_python from bugfix/g-to-10g to master

* commit 'e35e2a7127783180a4889304e3f98bebf6a71a0f':
  CreateInstance的datadisk参数单位改为10G，方便计费处理