The problem is that either you have not installed the MySQL client locally, or gcloud can't find it.
If you have not installed MySQL yet, follow the instructions to do so.
If you have installed MySQL but you're still getting this error, try entering mysql
at the shell prompt. If you get a command not found
error, MySQL is missing from your $PATH, and you need to figure out where it has been installed.
For example, on OS X, MySQL is by default installed in the directory /usr/local/mysql/bin/
. Add this to your $PATH, and it should start working:
export PATH=$PATH:/usr/local/mysql/bin/