Error if file listed in config.yml content section does not exist
Error if file listed in config.yml content section does not exist

(refs #9638)

milljm/moose,milljm/moose,SudiptaBiswas/moose,nuclear-wizard/moose,permcody/moose,milljm/moose,SudiptaBiswas/moose,sapitts/moose,permcody/moose,YaqiWang/moose,lindsayad/moose,jessecarterMOOSE/moose,nuclear-wizard/moose,jessecarterMOOSE/moose,idaholab/moose,sapitts/moose,laagesen/moose,permcody/moose,dschwen/moose,jessecarterMOOSE/moose,idaholab/moose,sapitts/moose,lindsayad/moose,bwspenc/moose,harterj/moose,lindsayad/moose,andrsd/moose,YaqiWang/moose,YaqiWang/moose,permcody/moose,idaholab/moose,sapitts/moose,andrsd/moose,laagesen/moose,idaholab/moose,bwspenc/moose,dschwen/moose,SudiptaBiswas/moose,andrsd/moose,dschwen/moose,milljm/moose,dschwen/moose,harterj/moose,YaqiWang/moose,jessecarterMOOSE/moose,SudiptaBiswas/moose,SudiptaBiswas/moose,laagesen/moose,harterj/moose,sapitts/moose,andrsd/moose,idaholab/moose,laagesen/moose,nuclear-wizard/moose,harterj/moose,bwspenc/moose,jessecarterMOOSE/moose,dschwen/moose,lindsayad/moose,bwspenc/moose,lindsayad/moose,andrsd/moose,bwspenc/moose,harterj/moose,laagesen/moose,nuclear-wizard/moose,milljm/moose