Description of problem:

It is a case when I check checkbox 'Use Proxy' in 'Register' Dialog but no fields related to proxy are filled.

Cockpit should verify that all proxy related fields in 'Register' dialog are filled.

If not, cockpit should display some message that proxy fields are required to fill.

you can see details in https://polarion.engineering.redhat.com/polarion/#/project/RedHatEnterpriseLinux7/workitem?id=RHEL7-104117&revision=5769679

Actual behaviour:

If I click on checkbox 'Use Proxy' and click on 'Register' button
then cockpit registers a system.

The right behaviour:

If I click on checkbox 'Use Proxy' and click on 'Register' button
then cockpit displays an error message 'You want to connect using proxy. Please fill informations about proxy connection to be used'