This change clarifies the documentation on
Resolve{TCP,UDP,IP,Unix}Addr to avoid unnecessary confusion about how
the arguments are used to make end point addresses.

Also replaces "name" or "hostname" with "host name" when the term
implies the use of DNS.

Updates #17613.

Change-Id: Id6be87fe2e4666eecd5b92f18ad8b9a6c50a2bd6
Reviewed-on: https://go-review.googlesource.com/34879Reviewed-by: Ian Lance Taylor <iant@golang.org>