Stop importing testing in the main binary (#2479)

* Stop importing testing in the main binary

Stop importing "testing" into the main binary:

* test/helpers.go imported it; remote that and change function signature
* update all tests that use this

Signed-off-by: Miek Gieben <miek@miek.nl>

* Drop import testing from metrics plugin

Signed-off-by: Miek Gieben <miek@miek.nl>

* more fiddling

Signed-off-by: Miek Gieben <miek@miek.nl>

test/ds_file_test.go

@@ -53,6 +53,8 @@ func TestLookupDS(t *testing.T) {
 			t.Fatalf("Expected to receive reply, but didn't for %s %d", tc.Qname, tc.Qtype)
 		}
 
-		mtest.SortAndCheck(t, resp, tc)
+		if err := mtest.SortAndCheck(resp, tc); err != nil {
+			t.Error(err)
+		}
 	}
 }