The container update process got further improved with PR #239. 
It now has all the features of the update script used with manual and .deb package based openHAB installations:
- show update notes and warnings during the update (based on update.lst)
- execute the update pre/post commands (based on update.lst)
- replace userdata system files with newer versions (based on userdata_sysfiles.lst)
- update KAR files in addons dir by downloading newer versions
- log the update output in update.log