common: Hold reference during processing of messages
common: Hold reference during processing of messages

This prevents use-after-free in tests, where a message triggers
the test completion.

Closes #2684
Reviewed-by: Peter <a316049dd34607c62d4611d63ab22a6454add223@redhat.com>

harishanand95/cockpit,vanloswang/cockpit,moolitayer/cockpit,harishanand95/cockpit,cockpit-project/cockpit,harishanand95/cockpit,moraleslazaro/cockpit,FireDrunk/cockpit,dperpeet/cockpit,andreasn/cockpit,haiyangd/cockpit_view,deryni/cockpit,moraleslazaro/cockpit,xhad/cockpit,larsu/cockpit,matobet/cockpit,garrett/cockpit,martinpitt/cockpit,zigitax/cockpit,jscotka/cockpit,matobet/cockpit,dperpeet/cockpit,Scribery/cockpit,larsu/cockpit,FireDrunk/cockpit,SotolitoLabs/cockpit,sgallagher/cockpit,harishanand95/cockpit,stefwalter/cockpit,martinpitt/cockpit,cockpituous/cockpit,deryni/cockpit,andreasn/cockpit,xhad/cockpit,jscotka/cockpit,mvollmer/cockpit,mareklibra/cockpit,SotolitoLabs/cockpit,sgallagher/cockpit,xhad/cockpit,Scribery/cockpit,mareklibra/cockpit,andreasn/cockpit,moolitayer/cockpit,larsu/cockpit,stefwalter/cockpit,haiyangd/cockpit_view,denysvitali/cockpit,mvollmer/cockpit,cockpit-project/cockpit,arilivigni/cockpit,larskarlitski/cockpit,mareklibra/cockpit,jscotka/cockpit,xhad/cockpit,mvollmer/cockpit,martinpitt/cockpit,haiyangd/cockpit_view,mareklibra/cockpit,deryni/cockpit,larskarlitski/cockpit,arilivigni/cockpit,matobet/cockpit,stefwalter/cockpit,michalskrivanek/cockpit,andreasn/cockpit,garrett/cockpit,Scribery/cockpit,dperpeet/cockpit,sgallagher/cockpit,michalskrivanek/cockpit,SotolitoLabs/cockpit,jscotka/cockpit,denysvitali/cockpit,denysvitali/cockpit,petervo/cockpit,cockpituous/cockpit,deryni/cockpit,petervo/cockpit,martinpitt/cockpit,petervo/cockpit,martinpitt/cockpit,harishanand95/cockpit,xhad/cockpit,cockpituous/cockpit,cockpituous/cockpit,cockpit-project/cockpit,xhad/cockpit,jscotka/cockpit,arilivigni/cockpit,SotolitoLabs/cockpit,andreasn/cockpit,vanloswang/cockpit,stefwalter/cockpit,mareklibra/cockpit,stefwalter/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,zigitax/cockpit,michalskrivanek/cockpit,Scribery/cockpit,petervo/cockpit,larskarlitski/cockpit,arilivigni/cockpit,haiyangd/cockpit_view,dperpeet/cockpit,Scribery/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,michalskrivanek/cockpit,larskarlitski/cockpit,andreasn/cockpit,michalskrivanek/cockpit,moolitayer/cockpit,jscotka/cockpit,FireDrunk/cockpit,zigitax/cockpit,petervo/cockpit,moolitayer/cockpit,petervo/cockpit,deryni/cockpit,moraleslazaro/cockpit,vanloswang/cockpit,larsu/cockpit,harishanand95/cockpit,garrett/cockpit,mvollmer/cockpit,vanloswang/cockpit,haiyangd/cockpit_view,vanloswang/cockpit,larskarlitski/cockpit,petervo/cockpit,moraleslazaro/cockpit,harishanand95/cockpit,FireDrunk/cockpit,dperpeet/cockpit,moraleslazaro/cockpit,matobet/cockpit,SotolitoLabs/cockpit,deryni/cockpit,SotolitoLabs/cockpit,dperpeet/cockpit,denysvitali/cockpit,sgallagher/cockpit,mareklibra/cockpit,denysvitali/cockpit,michalskrivanek/cockpit,stefwalter/cockpit,arilivigni/cockpit,sgallagher/cockpit,mareklibra/cockpit,larsu/cockpit,zigitax/cockpit,xhad/cockpit,larskarlitski/cockpit,dperpeet/cockpit,deryni/cockpit,zigitax/cockpit,larsu/cockpit,michalskrivanek/cockpit,arilivigni/cockpit,cockpit-project/cockpit,arilivigni/cockpit,stefwalter/cockpit,garrett/cockpit,sgallagher/cockpit,vanloswang/cockpit,SotolitoLabs/cockpit,Scribery/cockpit,moolitayer/cockpit,cockpituous/cockpit,andreasn/cockpit,vanloswang/cockpit,cockpit-project/cockpit,larskarlitski/cockpit,matobet/cockpit,matobet/cockpit,Scribery/cockpit,garrett/cockpit,FireDrunk/cockpit,sgallagher/cockpit