Turn c9 WordPress workspace server "ON" and paste this bash code in the c9 ide terminal and click "enter"

setup-wp-twentyseventeen-child-plugins.sh

#turn workspace server on ( "RUN" button), paste this into c9 terminal, and hit "enter"
SETUP_PATH="setup.sh"
cat >$SETUP_PATH <<'EOF'
#!/bin/bash
curl -O https://raw.githubusercontent.com/wp-cli/builds/gh-pages/phar/wp-cli.phar
chmod +x wp-cli.phar
sudo mv wp-cli.phar /usr/local/bin/wp
wp core install --url=https://$C9_HOSTNAME --title=QuickWP --admin_user=admin --admin_password=123456 --admin_email=$C9_EMAIL
wp option update my_option '{"site_url": "bar"}' --format=json
wp theme install twentyseventeen
wp scaffold child-theme twentyseventeen-child --parent_theme=twentyseventeen
wp core update
wp core update-db
#uncomment last 2 lines to install and activate plugins
#the plugin slug to install is the last part of plugin page in wp repo URL
#ex: https://wordpress.org/plugins/contact-form-7-to-database-extension --> contact-form-7-to-database-extension
plugins=(debug-bar query-monitor);
for i in ${plugins[@]}; do wp plugin install --activate $i; done
wp theme activate twentyseventeen-child
wp rewrite structure /%postname%/
c9 wp-content/themes/twentyseventeen-child/functions.php
EOF
chmod +x $SETUP_PATH
./$SETUP_PATH
rm $SETUP_PATH
phpmyadmin-ctl install

Video and more info how to use here