Clarify a comment which says we require KeyName - which is incorrect

The Nova create API requires a name, image, and flavor.  The key_name
is not mandatory.  Possibly in AWS InstanceType (flavor) is not
mandatory but it is with Nova.

blueprint native-nova-instance

Change-Id: I6f5a77d7999ea4d8e91402ae215179b982a947f6
Merge "Clarify a comment which says we require KeyName - which is incorrect"