[python][packagemetadata] Do not raise exception when non-standard dune.module keys are present
Manual backport of b4118fc5 (!1118 (merged))
This came up in relation to a Python setup with releases/2.8 so I have some interest in getting this backported (to get this my Python setup with dumux and opm-common work). The fix is however useful independent of the situation where it came up.
Edited by Timo Koch