Improve error message in listing extension (refs #9815)
Improve error message in listing extension (refs #9815)

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