Changed travis builds to use addons for getting MySql 5.6 in Trusty

.travis.yml

 sudo: required
 dist: trusty
-
+addons:
+  apt:
+    packages:
+    - mysql-server-5.6
+    - mysql-client-core-5.6
+    - mysql-client-5.6
 language: php
 php:
   - 5.5
@@ -44,13 +49,9 @@ before_script:
   - echo 'sendmail_path = "/usr/sbin/sendmail -t -i "' > $(php --ini|grep -m 1 "ini files in:"|cut -d ":" -f 2)/sendmail.ini
   # Disable xDebug
   - echo '' > ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/xdebug.ini
-  # Install MySQL 5.6, create DB for integration tests
+  # Create DB for integration tests
   - >
       sh -c "if [ '$TEST_SUITE' = 'integration_part_1' ] || [ '$TEST_SUITE' = 'integration_part_2' ] || [ '$TEST_SUITE' = 'integration_integrity' ]; then
-      sudo apt-get remove -y -qq --purge mysql-common mysql-server-5.5 mysql-server-core-5.5 mysql-client-5.5 mysql-client-core-5.5;
-      sudo apt-get -y -qq autoremove;
-      sudo apt-get -y -qq autoclean;
-      sudo apt-get install -y -qq mysql-server-5.6 mysql-client-5.6;
       mysql -uroot -e 'SET @@global.sql_mode = NO_ENGINE_SUBSTITUTION; CREATE DATABASE magento_integration_tests;';
       mv dev/tests/integration/etc/install-config-mysql.travis.php.dist dev/tests/integration/etc/install-config-mysql.php;
       fi"