acertmgr.py: use os.path.join() instead of string concatenations
acertmgr.py: use os.path.join() instead of string concatenations

Signed-off-by: Ralf Ramsauer <92f48d309cda194c8eda36aa8f9ae28c488fa208@ramses-pyramidenbau.de>

davidklaftenegger/acertmgr,moepman/acertmgr