Return error from zedrouter.init (instead of os.Exit)

zedrouter.Run() already calls log.Fatal (with os.Exit inside) when error
is returned from init() or run() methods.

Signed-off-by: Milan Lenco <milan@zededa.com>

pkg/pillar/cmd/zedrouter/zedrouter.go

@@ -244,22 +244,22 @@ func (z *zedrouter) init() (err error) {
 
 	z.peUsagePersist, err = persistcache.New(types.PersistCachePatchEnvelopesUsage)
 	if err != nil {
-		log.Fatal(err)
+		return err
 	}
 
 	// restore cached patchEnvelopeUsage counters
 	for _, key := range z.peUsagePersist.Objects() {
 		cached, err := z.peUsagePersist.Get(key)
 		if err != nil {
-			log.Fatal(err)
+			return err
 		}
 		buf := bytes.NewBuffer(cached)
 		dec := gob.NewDecoder(buf)
 
 		var peUsage types.PatchEnvelopeUsage
 
 		if err := dec.Decode(&peUsage); err != nil {
-			log.Fatal(err)
+			return err
 		}
 
 		z.patchEnvelopesUsage.Store(key, peUsage)