add more validation for server

[WofWca]

currently many providers are failing

Current output:

Error in arcor.de.md:
 Error Error in server definition:Unexpected key "username"
Error in blindzeln.org.md:
 Error Error in server definition:Unexpected key "username"
Error in c1.testrun.org.md:
 Error Error in server definition:Unexpected key "username"
Error in c2.testrun.org.md:
 Error Error in server definition:Unexpected key "username"
Error in c3.testrun.org.md:
 Error Error in server definition:Unexpected key "username"
Error in daleth.cafe.md:
 Error Error in server definition:Invalid Socket "TLS"
Error in disroot.md:
 Error Error in server definition:Unexpected key "username"
Error in e.email.md:
 Error Error in server definition:Unexpected key "username"
Error in example.com.md:
 Error Error in server definition:Unexpected key "username"
Error in infomaniak.com.md:
 Error Error in server definition:Unexpected key "username"
Error in mail.de.md:
 Error Error in server definition:Unexpected key "username"
Error in mailbox.org.md:
 Error Error in server definition:Unexpected key "username"
Error in mehl.cloud.md:
 Error Error in server definition:Invalid Socket "TLS"
Error in mehl.store.md:
 Error Error in server definition:Unexpected key "username"
Error in nine.testrun.org.md:
 Error Error in server definition:Unexpected key "username"
Error in nubo.coop.md:
 Error Error in server definition:Unexpected key "username"
Error in ouvaton.coop.md:
 Error Error in server definition:Unexpected key "username"
Error in purelymail.com.md:
 Error Error in server definition:Unexpected key "username"
Error in riseup.net.md:
 Error Error in server definition:Unexpected key "username"
Error in systemausfall.org.md:
 Error Error in server definition:Unexpected key "username"
Error in systemli.org.md:
 Error Error in server definition:Unexpected key "username"

[WofWca]

Uh oh, I should have been more clear.

This will make CI fail (until the providers are fixed)