generate-jobs: Fix missing osname variable

aum-offline-upgrade-branch is not generated with following error:
template variable not defined in aum-offline-upgrade-branch: 'osname' is undefined

Signed-off-by: Frédéric Danis <frederic.danis@collabora.com>

generate-jobs.py

@@ -198,6 +198,7 @@ class JobGenerator:
         variables['priority'] = self.args.priority
         variables['image_date'] = self.args.date
         variables['image_name'] = self.args.name
+        variables['osname'] = self.args.osname
 
         # Set variables passed with '-t'
         if self.args.template_vars: