Made 1-phase rDG compatible with variable-area
Made 1-phase rDG compatible with variable-area

Refs idaholab/relap-7#484

milljm/moose,jessecarterMOOSE/moose,milljm/moose,milljm/moose,idaholab/moose,laagesen/moose,bwspenc/moose,harterj/moose,dschwen/moose,andrsd/moose,sapitts/moose,lindsayad/moose,dschwen/moose,andrsd/moose,bwspenc/moose,sapitts/moose,laagesen/moose,andrsd/moose,jessecarterMOOSE/moose,lindsayad/moose,laagesen/moose,jessecarterMOOSE/moose,jessecarterMOOSE/moose,lindsayad/moose,idaholab/moose,milljm/moose,sapitts/moose,dschwen/moose,harterj/moose,milljm/moose,dschwen/moose,lindsayad/moose,jessecarterMOOSE/moose,idaholab/moose,harterj/moose,laagesen/moose,idaholab/moose,dschwen/moose,harterj/moose,lindsayad/moose,andrsd/moose,andrsd/moose,bwspenc/moose,bwspenc/moose,sapitts/moose,laagesen/moose,idaholab/moose,bwspenc/moose,sapitts/moose,harterj/moose