Change processor interface to include register metrics method, so pro…

…cessors get their cusrtom metrics registered into the agent server

gossip/processor.go

@@ -23,21 +23,25 @@ import (
 
 	"github.com/bbva/qed/log"
 	"github.com/bbva/qed/protocol"
+	"github.com/prometheus/client_golang/prometheus"
 )
 
 type Processor interface {
 	Process(*protocol.BatchSnapshots)
+	RegisterMetrics(*prometheus.Registry)
 }
 
 type FakeProcessor struct {
 }
 
-func (d FakeProcessor) Process(b *protocol.BatchSnapshots) {
-}
+func (d FakeProcessor) Process(b *protocol.BatchSnapshots)     {}
+func (d FakeProcessor) RegisterMetrics(r *prometheus.Registry) {}
 
 type DummyProcessor struct {
 }
 
+func (d DummyProcessor) RegisterMetrics(r *prometheus.Registry) {}
+
 func (d DummyProcessor) Process(b *protocol.BatchSnapshots) {
 	for i := 0; i < len(b.Snapshots); i++ {
 		res, err := http.Get(fmt.Sprintf("http://127.0.0.1:8888/stat/?nodeType=auditor&id=%d", b.Snapshots[0].Snapshot.Version))