Change the way how precompiled tar ball is copied to /afs/cern.ch/cms/generators/www/

Instead of doing automatic copy of precompiled powheg tar ball to the directory 
/afs/cern.ch/cms/generators/www/<scram_arch_version>/<beamenergy>TeV/powheg, now the precompiled 
tar ball is put in a local working directory after running the script create_lhe_powheg_all.sh. 
The MC contacts must put the tar balls in the afs directory by hand before running LHE production.