using a persistent onos, etcd, and kafka adapter panics

When performing basic sanity test.

{"level":"warn","ts":"2020-04-03T19:11:56.965Z","caller":"core/device_handler.go:1053","msg":"core-proxy-get-child-device-failed","instanceId":"adapter-open-olt-77fdcbbb86-r5q4f","pkg":"core","parentDevice":"6eea2703-1dd6-422a-a502-3a815150cc49","err":"rpc error: code = Unavailable desc = rpc error: code = NotFound desc = 6eea2703-1dd6-422a-a502-3a815150cc49","sn":"BBSM00000001","stacktrace":"github.com/opencord/voltha-lib-go/v3/pkg/log.logger.Warnw\n\t/go/src/github.com/opencord/voltha-openolt-adapter/vendor/github.com/opencord/voltha-lib-go/v3/pkg/log/log.go:595\ngithub.com/opencord/voltha-openolt-adapter/internal/pkg/core.(*DeviceHandler).onuDiscIndication\n\t/go/src/github.com/opencord/voltha-openolt-adapter/internal/pkg/core/device_handler.go:1053\ngithub.com/opencord/voltha-openolt-adapter/internal/pkg/core.(*DeviceHandler).handleIndication.func4\n\t/go/src/github.com/opencord/voltha-openolt-adapter/internal/pkg/core/device_handler.go:492"}

{"level":"warn","ts":"2020-04-03T19:11:56.965Z","caller":"core/device_handler.go:1053","msg":"core-proxy-get-child-device-failed","instanceId":"adapter-open-olt-77fdcbbb86-r5q4f","pkg":"core","parentDevice":"6eea2703-1dd6-422a-a502-3a815150cc49","err":"rpc error: code = Unavailable desc = rpc error: code = NotFound desc = 6eea2703-1dd6-422a-a502-3a815150cc49","sn":"BBSM00000001","stacktrace":"github.com/opencord/voltha-lib-go/v3/pkg/log.logger.Warnw\n\t/go/src/github.com/opencord/voltha-openolt-adapter/vendor/github.com/opencord/voltha-lib-go/v3/pkg/log/log.go:595\ngithub.com/opencord/voltha-openolt-adapter/internal/pkg/core.(*DeviceHandler).onuDiscIndication\n\t/go/src/github.com/opencord/voltha-openolt-adapter/internal/pkg/core/device_handler.go:1053\ngithub.com/opencord/voltha-openolt-adapter/internal/pkg/core.(*DeviceHandler).handleIndication.func4\n\t/go/src/github.com/opencord/voltha-openolt-adapter/internal/pkg/core/device_handler.go:492"}

{"level":"warn","ts":"2020-04-03T19:11:56.965Z","caller":"core/device_handler.go:1055","msg":"core-proxy-get-child-device-failed-with-code","instanceId":"adapter-open-olt-77fdcbbb86-r5q4f","pkg":"core","errCode":"Unavailable","sn":"BBSM00000001","stacktrace":"github.com/opencord/voltha-lib-go/v3/pkg/log.logger.Warnw\n\t/go/src/github.com/opencord/voltha-openolt-adapter/vendor/github.com/opencord/voltha-lib-go/v3/pkg/log/log.go:595\ngithub.com/opencord/voltha-openolt-adapter/internal/pkg/core.(*DeviceHandler).onuDiscIndication\n\t/go/src/github.com/opencord/voltha-openolt-adapter/internal/pkg/core/device_handler.go:1055\ngithub.com/opencord/voltha-openolt-adapter/internal/pkg/core.(*DeviceHandler).handleIndication.func4\n\t/go/src/github.com/opencord/voltha-openolt-adapter/internal/pkg/core/device_handler.go:492"}

panic: runtime error: index out of range [1] with length 1
goroutine 5249 [running]:github.com/opencord/voltha-openolt-adapter/internal/pkg/resourcemanager.(*OpenOltResourceMgr).FreePONResourcesForONU(0xc0003a20f0, 0x10f5de0, 0xc00003e1a8, 0x100000000, 0xc000000000) /go/src/github.com/opencord/voltha-openolt-adapter/internal/pkg/resourcemanager/resourcemanager.go:803 +0x81egithub.com/opencord/voltha-openolt-adapter/internal/pkg/core.(*DeviceHandler).clearUNIData(0xc0004e9200, 0x10f5de0, 0xc00003e1a8, 0xc000997c98, 0xc000164508, 0xc000a2a800) /go/src/github.com/opencord/voltha-openolt-adapter/internal/pkg/core/device_handler.go:1511 +0x60agithub.com/opencord/voltha-openolt-adapter/internal/pkg/core.(*DeviceHandler).cleanupDeviceResources(0xc0004e9200, 0x10f5de0, 0xc00003e1a8, 0xe508e0, 0xc00003a5f2) /go/src/github.com/opencord/voltha-openolt-adapter/internal/pkg/core/device_handler.go:1602 +0x2d6created by github.com/opencord/voltha-openolt-adapter/internal/pkg/core.(*DeviceHandler).DeleteDevice /go/src/github.com/opencord/voltha-openolt-adapter/internal/pkg/core/device_handler.go:1564 +0x147