Update Yum commands for EL8 and removal of EL6
Update Yum commands for EL8 and removal of EL6

matyasselmeci/htcondor-ce,brianhlin/htcondor-ce,brianhlin/htcondor-ce,matyasselmeci/htcondor-ce,matyasselmeci/htcondor-ce,brianhlin/htcondor-ce