Fix: Software Update config could contain circular reference
Fix: Software Update config could contain circular reference

Caused by a wrong variable usage. Fixed the usage and added a migration
step that fixes the circular reference if it exists. Bumping configuration
version to 2.

Fixes #946

JackGavin13/octoprint-test-not-finished,CapnBry/OctoPrint,leductan-nguyen/RaionPi,uuv/OctoPrint,mrbeam/OctoPrint,Javierma/OctoPrint-TFG,spapadim/OctoPrint,ErikDeBruijn/OctoPrint,EZ3-India/EZ-Remote,ryanneufeld/OctoPrint,nickverschoor/OctoPrint,beeverycreative/BEEweb,JackGavin13/octoprint-test-not-finished,MoonshineSG/OctoPrint,shaggythesheep/OctoPrint,nickverschoor/OctoPrint,chriskoz/OctoPrint,Jaesin/OctoPrint,Voxel8/OctoPrint,MoonshineSG/OctoPrint,MaxOLydian/OctoPrint,dragondgold/OctoPrint,MoonshineSG/OctoPrint,foosel/OctoPrint,EZ3-India/EZ-Remote,dansantee/OctoPrint,Mikk36/OctoPrint,nickverschoor/OctoPrint,leductan-nguyen/RaionPi,CapnBry/OctoPrint,foosel/OctoPrint,uuv/OctoPrint,dragondgold/OctoPrint,foosel/OctoPrint,nicanor-romero/OctoPrint,foosel/OctoPrint,SeveQ/OctoPrint,chriskoz/OctoPrint,eliasbakken/OctoPrint,javivi001/OctoPrint,Javierma/OctoPrint-TFG,Salandora/OctoPrint,shaggythesheep/OctoPrint,CapnBry/OctoPrint,MoonshineSG/OctoPrint,eddieparker/OctoPrint,senttech/OctoPrint,chriskoz/OctoPrint,nicanor-romero/OctoPrint,spapadim/OctoPrint,Javierma/OctoPrint-TFG,alex1818/OctoPrint,Jaesin/OctoPrint,shohei/Octoprint,Salandora/OctoPrint,eliasbakken/OctoPrint,bicephale/OctoPrint,chriskoz/OctoPrint,javivi001/OctoPrint,beeverycreative/BEEweb,MaxOLydian/OctoPrint,masterhou/OctoPrint,JackGavin13/octoprint-test-not-finished,ryanneufeld/OctoPrint,beeverycreative/BEEweb,Jaesin/OctoPrint,javivi001/OctoPrint,sstocker46/OctoPrint,Salandora/OctoPrint,ErikDeBruijn/OctoPrint,bicephale/OctoPrint,sstocker46/OctoPrint,JackGavin13/octoprint-test-not-finished,nickverschoor/OctoPrint,senttech/OctoPrint,mcanes/OctoPrint,nicanor-romero/OctoPrint,MaxOLydian/OctoPrint,eddieparker/OctoPrint,shohei/Octoprint,Javierma/OctoPrint-TFG,mcanes/OctoPrint,punkkeks/OctoPrint,senttech/OctoPrint,eddieparker/OctoPrint,alex1818/OctoPrint,EZ3-India/EZ-Remote,leductan-nguyen/RaionPi,bicephale/OctoPrint,Voxel8/OctoPrint,ryanneufeld/OctoPrint,masterhou/OctoPrint,Mikk36/OctoPrint,alex1818/OctoPrint,masterhou/OctoPrint,punkkeks/OctoPrint,Skeen/OctoPrint,dansantee/OctoPrint,dragondgold/OctoPrint,mrbeam/OctoPrint,sstocker46/OctoPrint,SeveQ/OctoPrint,CapnBry/OctoPrint,shohei/Octoprint,bicephale/OctoPrint,jneves/OctoPrint,punkkeks/OctoPrint,beeverycreative/BEEweb,Salandora/OctoPrint,shohei/Octoprint,Jaesin/OctoPrint,ErikDeBruijn/OctoPrint,spapadim/OctoPrint,mcanes/OctoPrint,mrbeam/OctoPrint,Mikk36/OctoPrint,EZ3-India/EZ-Remote,Voxel8/OctoPrint,Skeen/OctoPrint,shohei/Octoprint,senttech/OctoPrint,ryanneufeld/OctoPrint,leductan-nguyen/RaionPi,uuv/OctoPrint,dansantee/OctoPrint,Skeen/OctoPrint,shaggythesheep/OctoPrint,eliasbakken/OctoPrint,SeveQ/OctoPrint,jneves/OctoPrint,jneves/OctoPrint