VOLTHA ofagent-go does not return an error of flows, flows stay in PENDING_ADD

Currently the core does not allow forceful remove of PENDING_ADD flow though ONOS.

Fi the flow yielded an error during installation in the core, the flow is stuck in pending add in ONOS and when trying to remove it forcefully it does not get cleaned out.

Steps to reproduce.

1) bring up a clean VOLTHA + ONOS system

2) create a file named `fail_flow.json` (see attached)

3) push flow with

curl -X POST --user onos:rocks --header 'Content-Type: application/json' --header 'Accept: application/json' -d @fail_flow.json 'http://localhost:8181/onos/v1/flows?appId=org.opencord.olt'

4) see error in the core like 

{"level":"error","ts":"2020-03-03T14:57:38.065Z","msg":"no-route","instanceId":"voltha-rw-core-75c58d7f6b-jjlhr","caller":"flow_decomposer.decomposeFlow:480","inPortNo":0,"outPortNo":0,"error":"rpc error: code = FailedPrecondition desc = no downstream route from:0 to:0","stacktrace":"github.com/opencord/voltha-lib-go/v3/pkg/log.Errorw\n\t/go/src/vendor/github.com/opencord/voltha-lib-go/v3/pkg/log/log.go:757\ngithub.com/opencord/voltha-go/rw_core/flowdecomposition.(*FlowDecomposer).decomposeFlow\n\t/go/src/rw_core/flowdecomposition/flow_decomposer.go:480\ngithub.com/opencord/voltha-go/rw_core/flowdecomposition.(*FlowDecomposer).DecomposeRules\n\t/go/src/rw_core/flowdecomposition/flow_decomposer.go:62\ngithub.com/opencord/voltha-go/rw_core/core.(*LogicalDeviceAgent).flowAdd\n\t/go/src/rw_core/core/logical_device_agent.go:904\ngithub.com/opencord/voltha-go/rw_core/core.(*LogicalDeviceAgent).updateFlowTable\n\t/go/src/rw_core/core/logical_device_agent.go:594\ngithub.com/opencord/voltha-go/rw_core/core.(*LogicalDeviceManager).updateFlowTable\n\t/go/src/rw_core/core/logical_device_manager.go:564"}

5) try and remove the flow from ONOS

flows --remove bf0000c97c9c9e (this last is the id of the flow in pending add)

6) see no result