Ensures that the timestamp is set

This issue was first reported in intelsdi-x#1118 but didn't address the TimeStamp.  This commit does.

grpc/common/common.go

@@ -127,19 +127,24 @@ func (m *metric) Unit() string                  { return m.unit }
 
 // Convert common.Metric to core.Metric
 func ToCoreMetric(mt *Metric) core.Metric {
-	var lastAdvertisedTime time.Time
+	var lastAdvertisedTime, timeStamp time.Time
 	// if the lastAdvertisedTime is not set we handle.  -62135596800 represents the
 	// number of seconds from 0001-1970 and is the default value for time.Unix.
 	if mt.LastAdvertisedTime.Sec == int64(-62135596800) {
 		lastAdvertisedTime = time.Unix(time.Now().Unix(), int64(time.Now().Nanosecond()))
 	} else {
 		lastAdvertisedTime = time.Unix(mt.LastAdvertisedTime.Sec, mt.LastAdvertisedTime.Nsec)
 	}
+	if mt.Timestamp.Sec == int64(-62135596800) {
+		timeStamp = time.Unix(time.Now().Unix(), int64(time.Now().Nanosecond()))
+	} else {
+		timeStamp = time.Unix(mt.Timestamp.Sec, mt.Timestamp.Nsec)
+	}
 	ret := &metric{
 		namespace:          ToCoreNamespace(mt.Namespace),
 		version:            int(mt.Version),
 		tags:               mt.Tags,
-		timeStamp:          time.Unix(mt.Timestamp.Sec, mt.Timestamp.Nsec),
+		timeStamp:          timeStamp,
 		lastAdvertisedTime: lastAdvertisedTime,
 		config:             ConfigMapToConfig(mt.Config),
 		description:        mt.Description,