Set version AFTER a successful update

If an app upgrade failed, the core version will not be increased either
in the database. This will re-display the update page and make it
possible to redo the apps upgrade.

Note that any core repair routine must take into account that an update
might need to be redone again even though the core's DB state is already
the one of the new version.
Merge pull request #9819 from owncloud/updater-setversionafterupdate

Set version AFTER a successful update