Switch to subjectAltNames

[ikapelyukhin]

This is a follow-up to #57.

Currently during CA and server certificate generation we are using Common Name field, which seems to be deprecated (RFC2818 states: "Although the use of the Common Name is existing practice, it is deprecated and Certification Authorities are encouraged to use the dNSName instead.") and has a rather short maximum length of 26 characters.

Instead only subjectAltNames should be used, they should allow hostnames up to 256 characters long.

• Common Name should be left empty during certificate generation, for both the CA certificate and the server certificate.
• Common name field in the generation dialog should be dropped.
• Maximum length check needs to be implemented for subjectAltNames form fields.

[ngetahun]

I have created a kanban card here https://trello.com/c/jy27HDvo/4019-yast-rmt-switch-to-subjectaltnames

[ancorgs]

Since the yast2-smt package is developed and maintained by the SCC Team at SUSE, instead of the core YaST Team, I'm adding the "other-maintainer" label to this in order to help filtering the various list of issues.