Add default Host - @fqdn - when upgrading from HTTP/1.0 to 1.1

when performing protocol upgrade from http 1.0 to 1.1 Host header needs to be provided.

With this MR now whenever Host header is missing @fqdn variable will be used as default Host value.

Related to:

• gitlab-ce#25839
• #1924 (closed)
• https://github.com/golang/go/issues/13624