[Sahara] Do not request for nodegroup template if not present

There is no sense in API call to Sahara about nodegroup template
information in case if node group was created without template.

Change-Id: I4c79550b9c36da325d384f08b45dce0bca69a148
Closes-Bug: #1389868
Merge "[Sahara] Do not request for nodegroup template if not present"