logging: unify pkg/log and plugin/log (#2245)

Default to using pkg/log for all logging and use a fixed time prefix
which is RFC3339Millli (doesn't exist in time, so we just extended
RFC3339), i.e. Nano might be pushing it.

Logs go from:

2018/10/30 19:14:55 [INFO] CoreDNS-1.2.5
2018/10/30 19:14:55 [INFO] linux/amd64, go1.11,

to:

2018-10-30T19:10:07.547Z [INFO] CoreDNS-1.2.5
2018-10-30T19:10:07.547Z [INFO] linux/amd64, go1.11,

Which includes the timezone - which oddly the std log package doesn't
natively do.

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

plugin/log/setup.go

@@ -1,9 +1,6 @@
 package log
 
 import (
-	"log"
-	"os"
-
 	"github.com/coredns/coredns/core/dnsserver"
 	"github.com/coredns/coredns/plugin"
 	"github.com/coredns/coredns/plugin/pkg/response"
@@ -25,15 +22,6 @@ func setup(c *caddy.Controller) error {
 		return plugin.Error("log", err)
 	}
 
-	// Open the log files for writing when the server starts
-	c.OnStartup(func() error {
-		for i := 0; i < len(rules); i++ {
-			rules[i].Log = log.New(os.Stdout, "", 0)
-		}
-
-		return nil
-	})
-
 	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
 		return Logger{Next: next, Rules: rules, ErrorFunc: dnsserver.DefaultErrorFunc}
 	})