Add Service Principal parameters to the Add-AzureRMServiceEndpoint cmdlet

[miiitch]

This PR has 3 parts:

• add serviceEndpoint parameters in Add-AzureRMServiceEndpoint cmdlet: if the serviceEndPoint parameters are not specified, the Automatic mode is used
• the _trackProgress function is changed too to reflect the return code of the api (https://www.visualstudio.com/en-us/docs/integrate/api/endpoints/endpoints)
• the URL in the payload changed to https://management.azure.com

[DarqueWarrior]

In the future make sure all the unit tests still pass. One is failing with your change. I will update the test and merge your changes. To test simply run Invoke-Pester.

[miiitch]

Sorry for the test, I'll be more careful next time.