Merge pull request #1 from Azure/master

sync
Merge branch 'master' of github.com:guangyang/azure-sdk-tools-xplat
Merge branch 'dev' of https://github.com/WindowsAzure/azure-sdk-tools-xplat into login
improve login message about org id and service principal
Merge pull request #1348 from guangyang/login

improve message for "azure login"