This change renames {ipraw,tcp,udp,unix}_test.go to
{ipraw,tcp,udp,unix}sock_test.go for clarification. Also moves
NSS-related system configuration test helpers into main_conf_test.go and
main_noconf_test.go.

Change-Id: I28ba1e8ceda7b182ee3aa85f0ca3321388ba45e2
Reviewed-on: https://go-review.googlesource.com/19787Reviewed-by: Ian Lance Taylor <iant@golang.org>