SplitMeshAction: Respect .cpa file extension if present.
SplitMeshAction: Respect .cpa file extension if present.

Refs #11004.

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