ui: use real OS names

Change the operating system field type to EnumLabel
which is being already translated to the real name according to
Enum.properties resource file.

Change-Id: I8fa85225c09fd6c00783507a8df4e96e66e87180
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=895609
Signed-off-by: Roy Golan <rgolan@redhat.com>