net: simplify error messages in tests

This change simplifies unnecessarily redundant error messages in tests.
There's no need to worry any more because package APIs now return
consistent, self-descriptive error values.

Alos renames ambiguous test functions and makes use of test tables.

Change-Id: I7b61027607c4ae2a3cf605d08d58cf449fa27eb2
Reviewed-on: https://go-review.googlesource.com/9662
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
diff --git a/src/net/conf_test.go b/src/net/conf_test.go
index 43be546..01de0de 100644
--- a/src/net/conf_test.go
+++ b/src/net/conf_test.go
@@ -277,7 +277,7 @@
 		for _, ht := range tt.hostTests {
 			gotOrder := tt.c.hostLookupOrder(ht.host)
 			if gotOrder != ht.want {
-				t.Errorf("%s: useCgoLookupHost(%q) = %v; want %v", tt.name, ht.host, gotOrder, ht.want)
+				t.Errorf("%s: hostLookupOrder(%q) = %v; want %v", tt.name, ht.host, gotOrder, ht.want)
 			}
 		}
 	}