Merge branch 'mysql-password-ci' into 'master'

Allow empty Mysql password on CI

[ci skip]

See merge request !2558

.gitlab-ci.yml

-# This file is generated by GitLab CI
+image: "ruby:2.1"
+
+services:
+  - mysql:latest
+  - postgres:latest
+  - redis:latest
+
+variables:
+  MYSQL_ALLOW_EMPTY_PASSWORD: "1"
+
 before_script:
   - ./scripts/prepare_build.sh
   - ruby -v