Set MOOSE_DIR if the user doesn't have it
Set MOOSE_DIR if the user doesn't have it

(closes #9502)

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