In gui mode progress.relaunch is ineffective in scenarios.py

we need to raise an exception instead.

kano_updater/commands/install.py

@@ -308,7 +308,8 @@ def install_standard(progress, status):
     try:
         preup.run(progress)
     except Relaunch:
-        raise
+        progress.relaunch()
+        return False
     except Exception as err:
         logger.error("The pre-update scenarios failed.")
         logger.error(err.encode('utf-8'))
@@ -324,7 +325,8 @@ def install_standard(progress, status):
         postup.run(progress)
     except Relaunch:
         bump_system_version()
-        raise
+        progress.relaunch()
+        return False
     except Exception as err:
         logger.error("The post-update scenarios failed.")
         logger.error(err.encode('utf-8'))

kano_updater/scenarios.py

@@ -23,6 +23,7 @@
 from kano_updater.utils import install, remove_user_files, update_failed, \
     purge, rclocal_executable, migrate_repository, get_users, run_for_every_user
 from kano_updater.paths import PYLIBS_DIR, PYFALLBACK_DIR
+from kano_updater.progress import Relaunch
 
 
 SOURCES_DIR = '/etc/apt/sources.list.d'
@@ -1060,7 +1061,7 @@ def beta_3_15_0_to_beta_3_16_0(self, progress):
         apt_handle = AptWrapper.get_instance()
         apt_handle.refresh_instance()
         apt_handle.update(progress)
-        progress.relaunch()
+        raise Relaunch()
 
     def beta_3_16_0_to_beta_4_0_0(self, dummy_progress):
         ''' 4.0.0 is the first Debian Stretch version. All the work for