In your app-yaml file (as well as in mysite/settings.py), you have to provide the instance connection name of your CloudSQL instance. It is in the format:
[PROJECT_NAME]:[REGION_NAME]:[INSTANCE_NAME]
.
You can get this instance connection name by running the gcloud command gcloud sql instances describe [YOUR_INSTANCE_NAME]
and copy the value shown for connectionName. In your case it seems that you have copied the command itself instead of the connectionName value.
Alternatively, you can also get the instance connection name by going to your Developer Console > SQL and click on your instance. You'll find the instance connection name under the "Connect to this instance" section.