Update pixmaps/system-logo-white.png
    
    - Previously, it was using the string "CentOS 8". This is redundant in
      cockpit login screen that already has the string "CENTOS LINUX" near
      the login box. This update changes the system-logo-white.png image to
      hold the CentOS Logo so to provide a stronger visual identity in
      cockpit login screen.  The height of system-logo-white.png is
      important. It must be exactly 80px because that is the size cockpit
      CSS expects to correctly display it.