CORD-348 Fabric multicast support - error handling

Automatically failover to backup spine if
- ingress - transit link down
- transit - egress link down
- transit device down

Can recover from fatal error with human involved
- ingress switch down
- egress switch down
- all links to spine down

Scan through McastRouteStore when
- SR activate
- link up

Also include following features
- Use flow objective context in McastHandler
- Update Mcast VLAN config sample

Change-Id: I75007d9efd7646e7c4e57fa6d3fc6943543153cf
diff --git a/tools/package/config/samples/network-cfg-fabric-2x2-all.json b/tools/package/config/samples/network-cfg-fabric-2x2-all.json
index f21272e..5b6f036 100644
--- a/tools/package/config/samples/network-cfg-fabric-2x2-all.json
+++ b/tools/package/config/samples/network-cfg-fabric-2x2-all.json
@@ -228,6 +228,10 @@
         "org.onosproject.core" : {
             "core" : {
                 "linkDiscoveryMode" : "STRICT"
+            },
+            "multicast": {
+                "ingressVlan": "None",
+                "egressVlan": "None"
             }
         },
         "org.onosproject.segmentrouting" : {