Upgrade to AtlasSetup

I have changed the setup for my ATLAS jobs so it uses AtlasSetup (rather than AtlasLogin). The magic lines are:

RELEASE=xx.xx.xx
source $VO_ATLAS_SW_DIR/software/$RELEASE/cmtsite/asetup.sh AtlasOffline $RELEASE

VO_ATLAS_SW_DIR is set up automatically and you have to set RELEASE yourself. Since AtlasSetup is only available from Release 16 onwards, jobs going to sites without Release 16 will fail.