[TAP,UWS] Fix backup restoration. When restoring upload only, the error message:

```
RESTORATION Incorrect JSON format for the serialization of an uploaded file!
Caused by a org.json.JSONException: JSONObject["length"] not a string.
[...]

RESTORATION Incorrect JSON format for the DALIUpload labelled "xxx" of the job "xxxxxxxxx": "xxxxxxxx" is not pointing a job parameter representing a file!
[...]

RESTORATION Unexpected error while restoring the UWS!
Caused by a java.lang.NullPointerException: Missing UploadFile! => Can not build a DaliUpload instance.
[...]
```

Now, in case of grave error while restoring backup files, it will be just
disabled, instead of preventing start-up of the TAP service.
In case of non-grave error while restoring a job or a user, the failed job or
error won't be restored and then the restoration process will go on with the
other jobs/users.