Fixed the issue where the node could not start after executing `./bin/emqx data import [FILE]`.

And strongly bind apikey's `apikey_key` to `apikey_name`.
- `apikey_key` will generate a unique value from the given human-readable `apikey_name` when generating an apikey using dashboard.
- `apikey_name` will be a unique value generated by `apikey_key` when using bootstrap file to generate apikey, .