* Avoid pre-importing config_flows if the integration does support migration
Currently we pre-import the config flow module if it exists since
setting up the config entry required comparing the versions found
in the config_flow.py. We can avoid the pre-import if the integration
does not support async_migrate_entry which means we avoid loading
many config flows in memory at startup.
* cover
* fix missing block
* do not call directly
* its too fast now, the test gets more along
* Update homeassistant/loader.py
