Add --fast flag to update_and_rebuild_libmesh.sh
Add --fast flag to update_and_rebuild_libmesh.sh

The --fast flag skips the steps of removing the build directory and
configuring libmesh, so we do not allow other configure flags to be
passed in addition to --fast.  We also check that there is a
pre-existing build directory when the user passes --fast, you can't do
--fast the first time you build libmesh.

Refs #6741.

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