varnish: simplify host header handling
- always downcase and trim the port number of inbound host headers;
- only check aliases and servername once in vcl_recv; set a variable for matching in further vcl_* functions;
- ensure all further vcl_* functions indeed use the variable for matching
Test Plan
testing this in vagrant admin-rp1 worked fine
Migrated from D7703 (view on Phabricator)