Ensure x-backend-server header appears in all responses

To accomplish this we simply move the middleware closer to the front
of the list of MIDDLEWARE so that it is not skipped for redirects.

bedrock/settings/base.py

@@ -473,6 +473,7 @@ BASIC_AUTH_CREDS = config('BASIC_AUTH_CREDS', default='')
 MIDDLEWARE = [
     'allow_cidr.middleware.AllowCIDRMiddleware',
     'django.middleware.security.SecurityMiddleware',
+    'bedrock.mozorg.middleware.HostnameMiddleware',
     'django.middleware.http.ConditionalGetMiddleware',
     'corsheaders.middleware.CorsMiddleware',
     'bedrock.mozorg.middleware.VaryNoCacheMiddleware',
@@ -481,7 +482,6 @@ MIDDLEWARE = [
     'bedrock.redirects.middleware.RedirectsMiddleware',
     'bedrock.base.middleware.LocaleURLMiddleware',
     'bedrock.mozorg.middleware.ClacksOverheadMiddleware',
-    'bedrock.mozorg.middleware.HostnameMiddleware',
     'django.middleware.common.CommonMiddleware',
     'django.contrib.messages.middleware.MessageMiddleware',
     'bedrock.mozorg.middleware.CacheMiddleware',