Connection add should throw proper error instead of InternalError

[ramya-c3]

Environment info

• NooBaa Version: VERSION
• Platform: Kubernetes 1.14.1 | minikube 1.1.1 | OpenShift 4.1 | other: specify](Connection add command output is not proper #8791)

Actual behavior

1.# /usr/local/bin/noobaa-cli connection add --name conee3 --notification_protocol http --agent_request_object '{"host":"localhost","port":8080,"timeout":100}' --request_options_object '{"auth":"vYoaR9c9tU1pjmv+2wn2I9zO","path":"/webhook"}' 2>/dev/null
{
"error": {
"code": "InternalError",
"message": "The server encountered an internal error. Please retry the request",
"cause": "Error: configuration file already exists\n at Object.create_config_file (/usr/local/noobaa-core/src/util/native_fs_utils.js:316:25)\n at async ConfigFS.create_connection_config_file (/usr/local/noobaa-core/src/sdk/config_fs.js:1364:9)\n at async Object.add_connect_file (/usr/local/noobaa-core/src/util/notifications_util.js:599:5)\n at async connection_management (/usr/local/noobaa-core/src/cmd/manage_nsfs.js:752:20)\n at async main (/usr/local/noobaa-core/src/cmd/manage_nsfs.js:78:13)"
}
}

Expected behavior

1. Error should be proper

Steps to reproduce

More information - Screenshots / Logs / Other output