Create a process group for each test to allow for easier killing.
Create a process group for each test to allow for easier killing.

closes #7293

liuwenf/moose,Chuban/moose,sapitts/moose,liuwenf/moose,harterj/moose,backmari/moose,backmari/moose,jessecarterMOOSE/moose,harterj/moose,joshua-cogliati-inl/moose,permcody/moose,liuwenf/moose,milljm/moose,dschwen/moose,dschwen/moose,katyhuff/moose,liuwenf/moose,stimpsonsg/moose,bwspenc/moose,laagesen/moose,sapitts/moose,katyhuff/moose,permcody/moose,SudiptaBiswas/moose,liuwenf/moose,YaqiWang/moose,friedmud/moose,backmari/moose,andrsd/moose,sapitts/moose,SudiptaBiswas/moose,YaqiWang/moose,lindsayad/moose,jessecarterMOOSE/moose,laagesen/moose,nuclear-wizard/moose,milljm/moose,YaqiWang/moose,stimpsonsg/moose,harterj/moose,Chuban/moose,idaholab/moose,yipenggao/moose,stimpsonsg/moose,bwspenc/moose,andrsd/moose,andrsd/moose,dschwen/moose,andrsd/moose,jessecarterMOOSE/moose,jessecarterMOOSE/moose,milljm/moose,permcody/moose,permcody/moose,joshua-cogliati-inl/moose,laagesen/moose,lindsayad/moose,harterj/moose,andrsd/moose,harterj/moose,milljm/moose,friedmud/moose,laagesen/moose,jessecarterMOOSE/moose,nuclear-wizard/moose,sapitts/moose,bwspenc/moose,joshua-cogliati-inl/moose,milljm/moose,nuclear-wizard/moose,Chuban/moose,SudiptaBiswas/moose,idaholab/moose,SudiptaBiswas/moose,idaholab/moose,stimpsonsg/moose,dschwen/moose,lindsayad/moose,SudiptaBiswas/moose,sapitts/moose,bwspenc/moose,lindsayad/moose,YaqiWang/moose,friedmud/moose,idaholab/moose,dschwen/moose,Chuban/moose,lindsayad/moose,yipenggao/moose,friedmud/moose,yipenggao/moose,laagesen/moose,nuclear-wizard/moose,katyhuff/moose,yipenggao/moose,bwspenc/moose,backmari/moose,katyhuff/moose,joshua-cogliati-inl/moose,liuwenf/moose,idaholab/moose