[repo] ensure we don't restart a task while the repo is shutting down (closes #1942736)
we need a safety belt in cw itself again looping task which use 'try / except'
or doesn't need to access the db (which will trigger ShuttingDown exception)
# type attribute might already be there if migrating from
# version < 3.5 to version >= 3.5.3, BaseTransition being added
# in bootstrap_migration
if versions_map['cubicweb'][0] >= (3, 5, 0):
add_attribute('BaseTransition', 'type')
sync_schema_props_perms('state_of')
sync_schema_props_perms('transition_of')