OpenOnuAdapterGo: Panic during scale tests if large number of ONTS flap during ACTIVATION.

ONTs on a scale set up are in a continous flapping state and while the device is being configured for initial MIBs , a down indication might have been triggered a device deletion and clean up . Hence the omcicc object is invalid causing an exception.
This configuration is being performed in a separate goroutine and waits on OMCI responses which will eventually fire back after the timeout and meanwhile the device is deleted due to a down indication and LOS.

github.com/opencord/voltha-openonu-adapter-go/internal/pkg/common.(*OmciCC).confFailMeAlreadyHandled(0x0, 0xab, 0xc03280c300)
/go/src/internal/pkg/common/omci_cc.go:5275 +0x3d
github.com/opencord/voltha-openonu-adapter-go/internal/pkg/common.(*OmciCC).NotifyAboutOnuConfigFailure(0x0, 0x16d77c0, 0xc015aea720, 0x15161f5, 0x1a, 0x20200ab, 0xc02805d300, 0x3a, 0xc02a170500)
/go/src/internal/pkg/common/omci_cc.go:5257 +0x50
github.com/opencord/voltha-openonu-adapter-go/internal/pkg/mib.(*OnuDeviceEntry).waitforOmciResponse(0xc00ffffc00, 0x16d77c0, 0xc015aea720, 0xc000679b00, 0x3, 0xc02b507401)
/go/src/internal/pkg/mib/mib_download.go:393 +0x67c
github.com/opencord/voltha-openonu-adapter-go/internal/pkg/mib.(*OnuDeviceEntry).performInitialBridgeSetup(0xc00ffffc00, 0x16d77c0, 0xc015aea720)
/go/src/internal/pkg/mib/mib_download.go:371 +0x5fa
created by github.com/opencord/voltha-openonu-adapter-go/internal/pkg/mib.(*OnuDeviceEntry).enterBridgeInitState
/go/src/internal/pkg/mib/mib_download.go:93 +0x1b4