LLNG should not refuse logout when one OIDC/SAML SP fail to logout

Affected version

Version: %2.17.1

Summary

• Configure LLNG with one OIDC relying party with back channel logout
• Log-in and browse RP
• Shutdown RP
• Try to logout

Then LLNG just displays "Error" and refuse to logout

Propose behavior

• Unlog anyway from LLNG
• Display a message "Didn't succeed to logout from all applications, you should close your browser"