Configurable zone reload interval in file plugin (#2110)

* Configurable zone reload interval in file plugin

* passing reload config from auto plugin to file plugin. removed noReload property from Zone struct. fixed tests based on short file reload hack

plugin/file/zone.go

@@ -6,6 +6,7 @@ import (
 	"path"
 	"strings"
 	"sync"
+	"time"
 
 	"github.com/coredns/coredns/plugin/file/tree"
 	"github.com/coredns/coredns/plugin/pkg/upstream"
@@ -27,7 +28,8 @@ type Zone struct {
 	TransferFrom []string
 	Expired      *bool
 
-	NoReload       bool
+	ReloadInterval time.Duration
+	LastReloaded   time.Time
 	reloadMu       sync.RWMutex
 	reloadShutdown chan bool
 	Upstream       upstream.Upstream // Upstream for looking up names during the resolution process
@@ -50,6 +52,7 @@ func NewZone(name, file string) *Zone {
 		Tree:           &tree.Tree{},
 		Expired:        new(bool),
 		reloadShutdown: make(chan bool),
+		LastReloaded:   time.Now(),
 	}
 	*z.Expired = false
 
@@ -161,7 +164,7 @@ func (z *Zone) TransferAllowed(state request.Request) bool {
 // All returns all records from the zone, the first record will be the SOA record,
 // otionally followed by all RRSIG(SOA)s.
 func (z *Zone) All() []dns.RR {
-	if !z.NoReload {
+	if z.ReloadInterval > 0 {
 		z.reloadMu.RLock()
 		defer z.reloadMu.RUnlock()
 	}