ERROR 2003 (HY000): Can't connect to MySQL server on 'xxx.xxx.xx.xx' (10060)
I had a similar issue. I believe there are two ways to resolve it (though only one worked for me).

The first way (that did not work for me) would be to create a client certificate via the Cloud Platform -> SQL -> [Instance] -> Access Control tab -> SSL tab -> Create Client Certificate button.

It will give you instructions for downloading the client certificate to your machine and using it to connect via SSL.

The second way (which did work for me) was to allow non-SSL connections. You can find the button in the the "SSL Connections" section under the same SSL tab (under Access Control for the instance). Then try connecting with gcloud sql connect [instance-name] --user=root. This will automatically send a request to allow your IP address to connect directly to the database, and then attempt to connect via the mysql tool.