Added backup URL to scada

[WenzDaniel]

What does the code in this PR do / what does it improve?

Add backup url to SCADA. Requires a change of our config file, should be backwards compatible.

[jmosbacher]

I think this implementation is fine but if you feel like making some improvements I would:

1. use the base URL of the current sclogin_url as a default value so old configs still work
2. instead of having a url and backup_url configs, just parse the url (or base_url) config as a list with url.split(',') so that multiple URLs can be passed similar to the mongo url syntax
3. just do a for loop over the URL list and break on the first one that succeeds during login, then set the url to that one.

[ahiguera-mx]

@LuisSanchez25