title: Where to set DEFAULT_DB_ALIAS?
body: <p>I need to change used database configuration on application execute depending on environment. I have following configuration for db:</p>
  
  <pre><code>DATABASES = {
      'localhost': {
          'ENGINE': 'django.db.backends.sqlite3',
          'NAME': os.path.join(PROJECT_VAR, 'data/localhost.sqlite3'),
      },
      'test': {
          'ENGINE': 'django.db.backends.mysql', 
          'NAME': 'novumaz',
          'USER': 'novumaz',
          'PASSWORD': 'novumaz',
          'HOST': '',
          'PORT': '',
      },
      'production': {
          'ENGINE': 'django.db.backends.mysql', 
          'NAME': 'set database name',
          'USER': 'set database user name',
          'PASSWORD': 'set database user password',
          'HOST': '',
          'PORT': '',
      },
  }
  </code></pre>
  
  <p>Tried set it in wsgi.py and manage.py. Non of them works.</p>