[FS#370] Unable to do upgrade from a system built by image builder

[LEDE Bugs]

The following task is now closed:

FS#370 - Unable to do upgrade from a system built by image builder
User who did this - Mathias Kresin (mkresin)

Reason for closing: Fixed
Additional comments about closing: Fix with https://git.lede-project.org/38de638eae795f8843f84c0351c5f7f7f85b8361

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=370