title: Django read_default_file doesn't work
body: <p>I try to use read_defaul_file option but it doesn't work.</p>
  
  <pre><code>DATABASES = {
  'default': {
      'ENGINE': 'django.db.backends.mysql',
      'OPTIONS': {
          'read_default_file': '/vagrant/project/my.cnf'
      }
  }}
  </code></pre>
  
  <p>my.cnf </p>
  
  <pre><code>[client]
  database=db_2
  user=root
  password=root
  default-character-set=utf8
  [mysqld]
  character_set_client=utf8
  character_set_server=utf8
  collation_server=utf8_unicode_ci
  </code></pre>
  
  <p>When I pass settings as usual It works normally. But It doesn't read my.cnf file. File has 777 permissions.</p>