Make the test harness getCompilers() function work with either "installed" or "uninstalled" libmesh.
Make the test harness getCompilers() function work with either "installed" or "uninstalled" libmesh.

Refs #1665.

r16138

markr622/moose,nuclear-wizard/moose,waxmanr/moose,tonkmr/moose,wgapl/moose,capitalaslash/moose,harterj/moose,markr622/moose,backmari/moose,SudiptaBiswas/moose,mellis13/moose,SudiptaBiswas/moose,dschwen/moose,harterj/moose,milljm/moose,roystgnr/moose,bwspenc/moose,shanestafford/moose,bwspenc/moose,milljm/moose,harterj/moose,yipenggao/moose,katyhuff/moose,kasra83/moose,yipenggao/moose,YaqiWang/moose,jhbradley/moose,nuclear-wizard/moose,idaholab/moose,laagesen/moose,andrsd/moose,mellis13/moose,wgapl/moose,friedmud/moose,joshua-cogliati-inl/moose,xy515258/moose,sapitts/moose,jessecarterMOOSE/moose,adamLange/moose,sapitts/moose,capitalaslash/moose,capitalaslash/moose,adamLange/moose,permcody/moose,xy515258/moose,andrsd/moose,harterj/moose,joshua-cogliati-inl/moose,jbair34/moose,roystgnr/moose,roystgnr/moose,friedmud/moose,bwspenc/moose,friedmud/moose,waxmanr/moose,lindsayad/moose,idaholab/moose,idaholab/moose,jessecarterMOOSE/moose,liuwenf/moose,milljm/moose,cpritam/moose,milljm/moose,liuwenf/moose,capitalaslash/moose,giopastor/moose,giopastor/moose,lindsayad/moose,roystgnr/moose,xy515258/moose,raghavaggarwal/moose,permcody/moose,bwspenc/moose,apc-llc/moose,giopastor/moose,permcody/moose,permcody/moose,liuwenf/moose,kasra83/moose,jiangwen84/moose,jasondhales/moose,jessecarterMOOSE/moose,liuwenf/moose,cpritam/moose,YaqiWang/moose,stimpsonsg/moose,shanestafford/moose,Chuban/moose,zzyfisherman/moose,adamLange/moose,liuwenf/moose,jasondhales/moose,wgapl/moose,tonkmr/moose,laagesen/moose,dschwen/moose,yipenggao/moose,laagesen/moose,WilkAndy/moose,backmari/moose,tonkmr/moose,cpritam/moose,zzyfisherman/moose,apc-llc/moose,danielru/moose,jessecarterMOOSE/moose,tonkmr/moose,jiangwen84/moose,raghavaggarwal/moose,idaholab/moose,lindsayad/moose,jiangwen84/moose,SudiptaBiswas/moose,liuwenf/moose,zzyfisherman/moose,sapitts/moose,stimpsonsg/moose,andrsd/moose,shanestafford/moose,SudiptaBiswas/moose,yipenggao/moose,WilkAndy/moose,dschwen/moose,danielru/moose,harterj/moose,joshua-cogliati-inl/moose,markr622/moose,adamLange/moose,stimpsonsg/moose,roystgnr/moose,backmari/moose,lindsayad/moose,andrsd/moose,WilkAndy/moose,jinmm1992/moose,raghavaggarwal/moose,stimpsonsg/moose,mellis13/moose,katyhuff/moose,Chuban/moose,giopastor/moose,apc-llc/moose,danielru/moose,jbair34/moose,roystgnr/moose,lindsayad/moose,jasondhales/moose,shanestafford/moose,wgapl/moose,WilkAndy/moose,jasondhales/moose,jhbradley/moose,laagesen/moose,cpritam/moose,katyhuff/moose,nuclear-wizard/moose,shanestafford/moose,apc-llc/moose,tonkmr/moose,waxmanr/moose,dschwen/moose,jbair34/moose,cpritam/moose,bwspenc/moose,backmari/moose,laagesen/moose,roystgnr/moose,xy515258/moose,jinmm1992/moose,jinmm1992/moose,dschwen/moose,jhbradley/moose,kasra83/moose,zzyfisherman/moose,mellis13/moose,Chuban/moose,tonkmr/moose,SudiptaBiswas/moose,kasra83/moose,WilkAndy/moose,cpritam/moose,WilkAndy/moose,nuclear-wizard/moose,waxmanr/moose,zzyfisherman/moose,shanestafford/moose,sapitts/moose,YaqiWang/moose,idaholab/moose,jbair34/moose,markr622/moose,raghavaggarwal/moose,jiangwen84/moose,YaqiWang/moose,jessecarterMOOSE/moose,jinmm1992/moose,joshua-cogliati-inl/moose,milljm/moose,jhbradley/moose,andrsd/moose,katyhuff/moose,danielru/moose,friedmud/moose,Chuban/moose,zzyfisherman/moose,sapitts/moose