Fix cosmetic problems in YAML source

This change corrects problems reported by the `yamllint` linter.

Since key duplication problems were removed in 4d48711, this commit
mainly fixes trailing spaces and extra empty lines at beginning/end of
files.

test/integration/targets/mysql_user/defaults/main.yml

@@ -7,10 +7,9 @@ user_name_2: 'db_user2'
 user_password_1: '12345'
 user_password_2: '98765'
 
-db_names: 
+db_names:
     - clientdb
     - employeedb
     - providerdb
 
 tmp_dir: '/tmp'
-