Adds clarification note for project_id vs tenant_id

The client __init__ method takes both a project_id and tenant_id which is
rather confusing as in the Nova API these terms are used interchangeably. The
comment clarifies the difference between a project_id and tenant_id
when using novaclient.

For backwards compatibility reasons we can't really change the names (though for V3
perhaps we should in the future).

Change-Id: I569fe9318335c8d686153b0936205cb190e01ef1

novaclient/v1_1/client.py

@@ -92,6 +92,13 @@ class Client(object):
                   connection_pool=False, completion_cache=None):
         # FIXME(comstud): Rename the api_key argument above when we
         # know it's not being used as keyword argument
+
+        # NOTE(cyeoh): In the novaclient context (unlike Nova) the
+        # project_id is not the same as the tenant_id. Here project_id
+        # is a name (what the Nova API often refers to as a project or
+        # tenant name) and tenant_id is a UUID (what the Nova API
+        # often refers to as a project_id or tenant_id).
+
         password = api_key
         self.projectid = project_id
         self.tenant_id = tenant_id

novaclient/v3/client.py

@@ -75,6 +75,12 @@ class Client(object):
                   auth_plugin=None, auth_token=None,
                   cacert=None, tenant_id=None, user_id=None,
                   connection_pool=False, completion_cache=None):
+        # NOTE(cyeoh): In the novaclient context (unlike Nova) the
+        # project_id is not the same as the tenant_id. Here project_id
+        # is a name (what the Nova API often refers to as a project or
+        # tenant name) and tenant_id is a UUID (what the Nova API
+        # often refers to as a project_id or tenant_id).
+
         self.projectid = project_id
         self.tenant_id = tenant_id
         self.user_id = user_id