Replace custom install script with add-on

Following this documentation:
https://docs.travis-ci.com/user/database-setup/#mysql-57
found via https://stackoverflow.com/a/49542847/353612

.travis.yml

@@ -34,20 +34,41 @@ jobs:
     - stage: Test
       env: DB=mysql MYSQL_VERSION=5.7
       php: 7.1
+      addons:
+        apt:
+          sources:
+            - mysql-5.7-trusty
+          packages:
+            - mysql-server
+            - mysql-client
       before_script:
         - ./tests/travis/install-mysql-$MYSQL_VERSION.sh
       sudo: required
 
     - stage: Test
       env: DB=mysql MYSQL_VERSION=5.7
       php: 7.2
+      addons:
+        apt:
+          sources:
+            - mysql-5.7-trusty
+          packages:
+            - mysql-server
+            - mysql-client
       before_script:
         - ./tests/travis/install-mysql-$MYSQL_VERSION.sh
       sudo: required
 
     - stage: Test
       env: DB=mysql MYSQL_VERSION=5.7
       php: nightly
+      addons:
+        apt:
+          sources:
+            - mysql-5.7-trusty
+          packages:
+            - mysql-server
+            - mysql-client
       before_script:
         - ./tests/travis/install-mysql-$MYSQL_VERSION.sh
       sudo: required

tests/travis/install-mysql-5.7.sh

@@ -2,21 +2,5 @@
 
 set -ex
 
-echo "Installing MySQL 5.7..."
-
-sudo service mysql stop
-sudo apt-get remove "^mysql.*"
-sudo apt-get autoremove
-sudo apt-get autoclean
-echo mysql-apt-config mysql-apt-config/select-server select mysql-5.7 | sudo debconf-set-selections
-wget http://dev.mysql.com/get/mysql-apt-config_0.8.6-1_all.deb
-sudo DEBIAN_FRONTEND=noninteractive dpkg -i mysql-apt-config_0.8.6-1_all.deb
-sudo rm -rf /var/lib/apt/lists/*
-sudo apt-get clean
-sudo apt-get update -q
-sudo apt-get install -q -y -o Dpkg::Options::="--force-confdef" -o Dpkg::Options::="--force-confold" mysql-server libmysqlclient-dev
-sudo mysql_upgrade
-
 echo "Restart mysql..."
 sudo mysql -e "use mysql; update user set authentication_string=PASSWORD('') where User='root'; update user set plugin='mysql_native_password';FLUSH PRIVILEGES;"
-