TestFFIInvokeMethod - intermittent E2E test failure

Cause: `"error":"FF10315: Unable to resolve contract method: %!!(MISSING)s()"` - noting there's a secondary problem with a missing insert here, making diagnosis harder.

Example: https://github.com/hyperledger/firefly/runs/4910370346?check_suite_focus=true

```
2022-01-23T02:32:27.7485537Z === RUN TestEthereumE2ESuite/TestFFIInvokeMethod
2022-01-23T02:32:27.7486112Z e2e_test.go:198: Client 1: http://127.0.0.1:5000/api/v1
2022-01-23T02:32:27.7486657Z e2e_test.go:199: Client 2: http://127.0.0.1:5001/api/v1
2022-01-23T02:32:27.7487167Z restclient.go:65: ==> GET /namespaces map[]
2022-01-23T02:32:27.7527645Z restclient.go:72: <== 200
2022-01-23T02:32:27.7528061Z restclient.go:65: ==> GET /namespaces map[]
2022-01-23T02:32:27.7541284Z restclient.go:72: <== 200
2022-01-23T02:32:27.7541792Z restclient.go:65: ==> GET /network/organizations map[sort:[created]]
2022-01-23T02:32:27.7551847Z restclient.go:72: <== 200
2022-01-23T02:32:27.7552436Z restclient.go:65: ==> GET /network/organizations map[sort:[created]]
2022-01-23T02:32:27.7569180Z restclient.go:72: <== 200
2022-01-23T02:32:27.7570043Z e2e_test.go:231: Websocket 1: ws://127.0.0.1:5000/ws?namespace=default&ephemeral&autoack&filter.events=message_confirmed|token_pool_confirmed|token_transfer_confirmed|blockchain_event&changeevents=.*
2022-01-23T02:32:27.7574055Z e2e_test.go:232: Websocket 2: ws://127.0.0.1:5001/ws?namespace=default&ephemeral&autoack&filter.events=message_confirmed|token_pool_confirmed|token_transfer_confirmed|blockchain_event&changeevents=.*
2022-01-23T02:32:27.7596071Z restclient.go:65: ==> POST /namespaces/default/contracts/subscriptions map[]
2022-01-23T02:32:27.7655123Z e2e_test.go:262: Websocket 127.0.0.1:5000 receive: {"type":"change_notification","change":{"collection":"contractsubscriptions","type":"created","namespace":"default","id":"e1fd1cf2-054f-40c7-b89e-5a6bee3d8711"}}
2022-01-23T02:32:27.7655700Z restclient.go:72: <== 200
2022-01-23T02:32:27.7656241Z restclient.go:65: ==> GET /namespaces/default/contracts/subscriptions map[created:[>1642905147747211109]]
2022-01-23T02:32:27.7658106Z restclient.go:72: <== 200
2022-01-23T02:32:28.7499573Z e2e_test.go:262: Websocket 127.0.0.1:5000 receive: {"type":"change_notification","change":{"collection":"contractevents","type":"created","namespace":"default","id":"e9957ccc-d736-4f58-ad7a-d93a4664925f","sequence":27}}
2022-01-23T02:32:28.7502622Z e2e_test.go:262: Websocket 127.0.0.1:5000 receive: {"type":"change_notification","change":{"collection":"events","type":"created","namespace":"default","id":"fef1cfcd-a781-4ac5-a0e0-a754a56ecbf7","sequence":64}}
2022-01-23T02:32:28.7554987Z e2e_test.go:262: Websocket 127.0.0.1:5000 receive: {"type":"change_notification","change":{"collection":"contractevents","type":"created","namespace":"default","id":"7546f60c-09c2-48ad-8a0f-a1d5c1ba8a19","sequence":28}}
2022-01-23T02:32:28.7556725Z e2e_test.go:262: Websocket 127.0.0.1:5000 receive: {"type":"change_notification","change":{"collection":"events","type":"created","namespace":"default","id":"900f6536-4d5e-40bf-b20f-ad957195699b","sequence":65}}
2022-01-23T02:32:28.7575887Z e2e_test.go:262: Websocket 127.0.0.1:5000 receive: {"id":"fef1cfcd-a781-4ac5-a0e0-a754a56ecbf7","sequence":64,"type":"blockchain_event","namespace":"default","reference":"e9957ccc-d736-4f58-ad7a-d93a4664925f","created":"2022-01-23T02:32:28.746050682Z","subscription":{"id":"2d127c47-2166-463e-beed-a30fffe134d4","namespace":"default","name":"2d127c47-2166-463e-beed-a30fffe134d4"}}
2022-01-23T02:32:28.7577233Z restclient.go:65: ==> POST /namespaces/default/contracts/interfaces/63cc9d1e-03bb-4693-b54a-ea208df2e720/invoke/set map[]
2022-01-23T02:32:28.7587234Z e2e_test.go:262: Websocket 127.0.0.1:5000 receive: {"id":"900f6536-4d5e-40bf-b20f-ad957195699b","sequence":65,"type":"blockchain_event","namespace":"default","reference":"7546f60c-09c2-48ad-8a0f-a1d5c1ba8a19","created":"2022-01-23T02:32:28.751218676Z","subscription":{"id":"2d127c47-2166-463e-beed-a30fffe134d4","namespace":"default","name":"2d127c47-2166-463e-beed-a30fffe134d4"}}
2022-01-23T02:32:28.7637487Z restclient.go:72: <== 400
2022-01-23T02:32:28.7638067Z restclient.go:74: 127.0.0.1:5000: use of closed network connection
2022-01-23T02:32:28.7653070Z e2e_test.go:247: WebSockets closed
2022-01-23T02:32:28.7653458Z --- FAIL: TestEthereumE2ESuite (95.10s)
```