Fix panic in metrics service in collector

There is no metrics partitioner running in collector.  This service
needs to be reworked since it has ingestor specific bits in it that
are not relevant for collector to run.

metrics/service.go

@@ -82,17 +82,20 @@ func (s *service) collect(ctx context.Context) {
 		case <-ctx.Done():
 			return
 		case <-t.C:
-			// Only one node should execute the cardinality counts so see if we are the owner.
-			hostname, _ := s.partitioner.Owner([]byte("AdxmonIngestorTableCardinalityCount"))
-			if s.kustoCli != nil && hostname == s.hostname {
-				stmt := kusto.NewStmt("", kusto.UnsafeStmt(unsafe.Stmt{Add: true, SuppressWarning: true})).UnsafeAdd(
-					".set-or-append async AdxmonIngestorTableCardinalityCount <| CountCardinality",
-				)
-				iter, err := s.kustoCli.Mgmt(ctx, s.database, stmt)
-				if err != nil {
-					logger.Error("Failed to execute cardinality counts: %s", err)
-				} else {
-					iter.Stop()
+			// This is only set when running on ingestor currently.
+			if s.partitioner != nil {
+				// Only one node should execute the cardinality counts so see if we are the owner.
+				hostname, _ := s.partitioner.Owner([]byte("AdxmonIngestorTableCardinalityCount"))
+				if s.kustoCli != nil && hostname == s.hostname {
+					stmt := kusto.NewStmt("", kusto.UnsafeStmt(unsafe.Stmt{Add: true, SuppressWarning: true})).UnsafeAdd(
+						".set-or-append async AdxmonIngestorTableCardinalityCount <| CountCardinality",
+					)
+					iter, err := s.kustoCli.Mgmt(ctx, s.database, stmt)
+					if err != nil {
+						logger.Error("Failed to execute cardinality counts: %s", err)
+					} else {
+						iter.Stop()
+					}
 				}
 			}